diff options
Diffstat (limited to 'old')
| -rw-r--r-- | old/vgmld10.txt | 6283 | ||||
| -rw-r--r-- | old/vgmld10.zip | bin | 0 -> 127277 bytes |
2 files changed, 6283 insertions, 0 deletions
diff --git a/old/vgmld10.txt b/old/vgmld10.txt new file mode 100644 index 0000000..77cc80a --- /dev/null +++ b/old/vgmld10.txt @@ -0,0 +1,6283 @@ +Project Gutenberg Etext Formation of Vegetable Mould, by Darwin +#9 in our series by Charles Darwin + + +Copyright laws are changing all over the world, be sure to check +the copyright laws for your country before posting these files!! + +Please take a look at the important information in this header. +We encourage you to keep this file on your own disk, keeping an +electronic path open for the next readers. Do not remove this. + + +**Welcome To The World of Free Plain Vanilla Electronic Texts** + +**Etexts Readable By Both Humans and By Computers, Since 1971** + +*These Etexts Prepared By Hundreds of Volunteers and Donations* + +Information on contacting Project Gutenberg to get Etexts, and +further information is included below. We need your donations. + + +The Formation of Vegetable Mould through the action of worms with +observations of their habits + +by Charles Darwin + +October, 2000 [Etext #2355] + + +Project Gutenberg Etext Formation of Vegetable Mould, by Darwin +*****This file should be named vgmld10.txt or vgmld10.zip****** + +Corrected EDITIONS of our etexts get a new NUMBER, vgmld11.txt +VERSIONS based on separate sources get new LETTER, vgmld10a.txt + + +Scanned and proofed by David Price +ccx074@coventry.ac.uk + +Project Gutenberg Etexts are usually created from multiple editions, +all of which are in the Public Domain in the United States, unless a +copyright notice is included. Therefore, we usually do NOT keep any +of these books in compliance with any particular paper edition. + + +We are now trying to release all our books one month in advance +of the official release dates, leaving time for better editing. + +Please note: neither this list nor its contents are final till +midnight of the last day of the month of any such announcement. +The official release date of all Project Gutenberg Etexts is at +Midnight, Central Time, of the last day of the stated month. A +preliminary version may often be posted for suggestion, comment +and editing by those who wish to do so. To be sure you have an +up to date first edition [xxxxx10x.xxx] please check file sizes +in the first week of the next month. Since our ftp program has +a bug in it that scrambles the date [tried to fix and failed] a +look at the file size will have to do, but we will try to see a +new copy has at least one byte more or less. + + +Information about Project Gutenberg (one page) + +We produce about two million dollars for each hour we work. The +time it takes us, a rather conservative estimate, is fifty hours +to get any etext selected, entered, proofread, edited, copyright +searched and analyzed, the copyright letters written, etc. This +projected audience is one hundred million readers. If our value +per text is nominally estimated at one dollar then we produce $2 +million dollars per hour this year as we release thirty-six text +files per month, or 432 more Etexts in 1999 for a total of 2000+ +If these reach just 10% of the computerized population, then the +total should reach over 200 billion Etexts given away this year. + +The Goal of Project Gutenberg is to Give Away One Trillion Etext +Files by December 31, 2001. [10,000 x 100,000,000 = 1 Trillion] +This is ten thousand titles each to one hundred million readers, +which is only ~5% of the present number of computer users. + +At our revised rates of production, we will reach only one-third +of that goal by the end of 2001, or about 3,333 Etexts unless we +manage to get some real funding; currently our funding is mostly +from Michael Hart's salary at Carnegie-Mellon University, and an +assortment of sporadic gifts; this salary is only good for a few +more years, so we are looking for something to replace it, as we +don't want Project Gutenberg to be so dependent on one person. + +We need your donations more than ever! + + +All donations should be made to "Project Gutenberg/CMU": and are +tax deductible to the extent allowable by law. (CMU = Carnegie- +Mellon University). + +For these and other matters, please mail to: + +Project Gutenberg +P. O. Box 2782 +Champaign, IL 61825 + +When all other email fails. . .try our Executive Director: +Michael S. Hart <hart@pobox.com> +hart@pobox.com forwards to hart@prairienet.org and archive.org +if your mail bounces from archive.org, I will still see it, if +it bounces from prairienet.org, better resend later on. . . . + +We would prefer to send you this information by email. + +****** + +To access Project Gutenberg etexts, use any Web browser +to view http://promo.net/pg. This site lists Etexts by +author and by title, and includes information about how +to get involved with Project Gutenberg. You could also +download our past Newsletters, or subscribe here. This +is one of our major sites, please email hart@pobox.com, +for a more complete list of our various sites. + +To go directly to the etext collections, use FTP or any +Web browser to visit a Project Gutenberg mirror (mirror +sites are available on 7 continents; mirrors are listed +at http://promo.net/pg). + +Mac users, do NOT point and click, typing works better. + +Example FTP session: + +ftp sunsite.unc.edu +login: anonymous +password: your@login +cd pub/docs/books/gutenberg +cd etext90 through etext99 +dir [to see files] +get or mget [to get files. . .set bin for zip files] +GET GUTINDEX.?? [to get a year's listing of books, e.g., GUTINDEX.99] +GET GUTINDEX.ALL [to get a listing of ALL books] + +*** + +**Information prepared by the Project Gutenberg legal advisor** + +(Three Pages) + + +***START**THE SMALL PRINT!**FOR PUBLIC DOMAIN ETEXTS**START*** +Why is this "Small Print!" statement here? You know: lawyers. +They tell us you might sue us if there is something wrong with +your copy of this etext, even if you got it for free from +someone other than us, and even if what's wrong is not our +fault. So, among other things, this "Small Print!" statement +disclaims most of our liability to you. It also tells you how +you can distribute copies of this etext if you want to. + +*BEFORE!* YOU USE OR READ THIS ETEXT +By using or reading any part of this PROJECT GUTENBERG-tm +etext, you indicate that you understand, agree to and accept +this "Small Print!" statement. If you do not, you can receive +a refund of the money (if any) you paid for this etext by +sending a request within 30 days of receiving it to the person +you got it from. If you received this etext on a physical +medium (such as a disk), you must return it with your request. + +ABOUT PROJECT GUTENBERG-TM ETEXTS +This PROJECT GUTENBERG-tm etext, like most PROJECT GUTENBERG- +tm etexts, is a "public domain" work distributed by Professor +Michael S. Hart through the Project Gutenberg Association at +Carnegie-Mellon University (the "Project"). Among other +things, this means that no one owns a United States copyright +on or for this work, so the Project (and you!) can copy and +distribute it in the United States without permission and +without paying copyright royalties. Special rules, set forth +below, apply if you wish to copy and distribute this etext +under the Project's "PROJECT GUTENBERG" trademark. + +To create these etexts, the Project expends considerable +efforts to identify, transcribe and proofread public domain +works. Despite these efforts, the Project's etexts and any +medium they may be on may contain "Defects". Among other +things, Defects may take the form of incomplete, inaccurate or +corrupt data, transcription errors, a copyright or other +intellectual property infringement, a defective or damaged +disk or other etext medium, a computer virus, or computer +codes that damage or cannot be read by your equipment. + +LIMITED WARRANTY; DISCLAIMER OF DAMAGES +But for the "Right of Replacement or Refund" described below, +[1] the Project (and any other party you may receive this +etext from as a PROJECT GUTENBERG-tm etext) disclaims all +liability to you for damages, costs and expenses, including +legal fees, and [2] YOU HAVE NO REMEDIES FOR NEGLIGENCE OR +UNDER STRICT LIABILITY, OR FOR BREACH OF WARRANTY OR CONTRACT, +INCLUDING BUT NOT LIMITED TO INDIRECT, CONSEQUENTIAL, PUNITIVE +OR INCIDENTAL DAMAGES, EVEN IF YOU GIVE NOTICE OF THE +POSSIBILITY OF SUCH DAMAGES. + +If you discover a Defect in this etext within 90 days of +receiving it, you can receive a refund of the money (if any) +you paid for it by sending an explanatory note within that +time to the person you received it from. If you received it +on a physical medium, you must return it with your note, and +such person may choose to alternatively give you a replacement +copy. If you received it electronically, such person may +choose to alternatively give you a second opportunity to +receive it electronically. + +THIS ETEXT IS OTHERWISE PROVIDED TO YOU "AS-IS". NO OTHER +WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED, ARE MADE TO YOU AS +TO THE ETEXT OR ANY MEDIUM IT MAY BE ON, INCLUDING BUT NOT +LIMITED TO WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A +PARTICULAR PURPOSE. + +Some states do not allow disclaimers of implied warranties or +the exclusion or limitation of consequential damages, so the +above disclaimers and exclusions may not apply to you, and you +may have other legal rights. + +INDEMNITY +You will indemnify and hold the Project, its directors, +officers, members and agents harmless from all liability, cost +and expense, including legal fees, that arise directly or +indirectly from any of the following that you do or cause: +[1] distribution of this etext, [2] alteration, modification, +or addition to the etext, or [3] any Defect. + +DISTRIBUTION UNDER "PROJECT GUTENBERG-tm" +You may distribute copies of this etext electronically, or by +disk, book or any other medium if you either delete this +"Small Print!" and all other references to Project Gutenberg, +or: + +[1] Only give exact copies of it. Among other things, this + requires that you do not remove, alter or modify the + etext or this "small print!" statement. You may however, + if you wish, distribute this etext in machine readable + binary, compressed, mark-up, or proprietary form, + including any form resulting from conversion by word pro- + cessing or hypertext software, but only so long as + *EITHER*: + + [*] The etext, when displayed, is clearly readable, and + does *not* contain characters other than those + intended by the author of the work, although tilde + (~), asterisk (*) and underline (_) characters may + be used to convey punctuation intended by the + author, and additional characters may be used to + indicate hypertext links; OR + + [*] The etext may be readily converted by the reader at + no expense into plain ASCII, EBCDIC or equivalent + form by the program that displays the etext (as is + the case, for instance, with most word processors); + OR + + [*] You provide, or agree to also provide on request at + no additional cost, fee or expense, a copy of the + etext in its original plain ASCII form (or in EBCDIC + or other equivalent proprietary form). + +[2] Honor the etext refund and replacement provisions of this + "Small Print!" statement. + +[3] Pay a trademark license fee to the Project of 20% of the + net profits you derive calculated using the method you + already use to calculate your applicable taxes. If you + don't derive profits, no royalty is due. Royalties are + payable to "Project Gutenberg Association/Carnegie-Mellon + University" within the 60 days following each + date you prepare (or were legally required to prepare) + your annual (or equivalent periodic) tax return. + +WHAT IF YOU *WANT* TO SEND MONEY EVEN IF YOU DON'T HAVE TO? +The Project gratefully accepts contributions in money, time, +scanning machines, OCR software, public domain etexts, royalty +free copyright licenses, and every other sort of contribution +you can think of. Money should be paid to "Project Gutenberg +Association / Carnegie-Mellon University". + +*END*THE SMALL PRINT! FOR PUBLIC DOMAIN ETEXTS*Ver.04.29.93*END* + + + + + +Scanned and proofed by David Price +ccx074@coventry.ac.uk + + + + + +THE FORMATION OF VEGETABLE MOULD +THROUGH THE ACTION OF WORMS +WITH OBSERVATIONS ON THEIR HABITS. + +by Charles Darwin + + + + +INTRODUCTION. + + + +The share which worms have taken in the formation of the layer of +vegetable mould, which covers the whole surface of the land in +every moderately humid country, is the subject of the present +volume. This mould is generally of a blackish colour and a few +inches in thickness. In different districts it differs but little +in appearance, although it may rest on various subsoils. The +uniform fineness of the particles of which it is composed is one of +its chief characteristic features; and this may be well observed in +any gravelly country, where a recently-ploughed field immediately +adjoins one which has long remained undisturbed for pasture, and +where the vegetable mould is exposed on the sides of a ditch or +hole. The subject may appear an insignificant one, but we shall +see that it possesses some interest; and the maxim "de minimis non +curat lex," does not apply to science. Even Elie de Beaumont, who +generally undervalues small agencies and their accumulated effects, +remarks: {1} "La couche tres-mince de la terre vegetale est un +monument d'une haute antiquite, et, par le fait de sa permanence, +un objet digne d'occuper le geologue, et capable de lui fournir des +remarques interessantes." Although the superficial layer of +vegetable mould as a whole no doubt is of the highest antiquity, +yet in regard to its permanence, we shall hereafter see reason to +believe that its component particles are in most cases removed at +not a very slow rate, and are replaced by others due to the +disintegration of the underlying materials. + +As I was led to keep in my study during many months worms in pots +filled with earth, I became interested in them, and wished to learn +how far they acted consciously, and how much mental power they +displayed. I was the more desirous to learn something on this +head, as few observations of this kind have been made, as far as I +know, on animals so low in the scale of organization and so poorly +provided with sense-organs, as are earth-worms. + +In the year 1837, a short paper was read by me before the +Geological Society of London, {2} "On the Formation of Mould," in +which it was shown that small fragments of burnt marl, cinders, +&c., which had been thickly strewed over the surface of several +meadows, were found after a few years lying at the depth of some +inches beneath the turf, but still forming a layer. This apparent +sinking of superficial bodies is due, as was first suggested to me +by Mr. Wedgwood of Maer Hall in Staffordshire, to the large +quantity of fine earth continually brought up to the surface by +worms in the form of castings. These castings are sooner or later +spread out and cover up any object left on the surface. I was thus +led to conclude that all the vegetable mould over the whole country +has passed many times through, and will again pass many times +through, the intestinal canals of worms. Hence the term "animal +mould" would be in some respects more appropriate than that +commonly used of "vegetable mould." + +Ten years after the publication of my paper, M. D'Archiac, +evidently influenced by the doctrines of Elie de Beaumont, wrote +about my "singuliere theorie," and objected that it could apply +only to "les prairies basses et humides;" and that "les terres +labourees, les bois, les prairies elevees, n'apportent aucune +preuve a l'appui de cette maniere de voir." {3} But M. D'Archiac +must have thus argued from inner consciousness and not from +observation, for worms abound to an extraordinary degree in kitchen +gardens where the soil is continually worked, though in such loose +soil they generally deposit their castings in any open cavities or +within their old burrows instead of on the surface. Hensen +estimates that there are about twice as many worms in gardens as in +corn-fields. {4} With respect to "prairies elevees," I do not know +how it may be in France, but nowhere in England have I seen the +ground so thickly covered with castings as on commons, at a height +of several hundred feet above the sea. In woods again, if the +loose leaves in autumn are removed, the whole surface will be found +strewed with castings. Dr. King, the superintendent of the Botanic +Garden in Calcutta, to whose kindness I am indebted for many +observations on earth-worms, informs me that he found, near Nancy +in France, the bottom of the State forests covered over many acres +with a spongy layer, composed of dead leaves and innumerable worm- +castings. He there heard the Professor of "Amenagement des Forets" +lecturing to his pupils, and pointing out this case as a "beautiful +example of the natural cultivation of the soil; for year after year +the thrown-up castings cover the dead leaves; the result being a +rich humus of great thickness." + +In the year 1869, Mr. Fish {5} rejected my conclusions with respect +to the part which worms have played in the formation of vegetable +mould, merely on account of their assumed incapacity to do so much +work. He remarks that "considering their weakness and their size, +the work they are represented to have accomplished is stupendous." +Here we have an instance of that inability to sum up the effects of +a continually recurrent cause, which has often retarded the +progress of science, as formerly in the case of geology, and more +recently in that of the principle of evolution. + +Although these several objections seemed to me to have no weight, +yet I resolved to make more observations of the same kind as those +published, and to attack the problem on another side; namely, to +weigh all the castings thrown up within a given time in a measured +space, instead of ascertaining the rate at which objects left on +the surface were buried by worms. But some of my observations have +been rendered almost superfluous by an admirable paper by Hensen, +already alluded to, which appeared in 1877. {6} Before entering on +details with respect to the castings, it will be advisable to give +some account of the habits of worms from my own observations and +from those of other naturalists. + +[FIRST EDITION, October 10th, 1881.] + + + +CHAPTER I--HABITS OF WORMS. + + + +Nature of the sites inhabited--Can live long under water-- +Nocturnal--Wander about at night--Often lie close to the mouths of +their burrows, and are thus destroyed in large numbers by birds-- +Structure--Do not possess eyes, but can distinguish between light +and darkness--Retreat rapidly when brightly illuminated, not by a +reflex action--Power of attention--Sensitive to heat and cold-- +Completely deaf--Sensitive to vibrations and to touch--Feeble power +of smell--Taste--Mental qualities--Nature of food--Omnivorous-- +Digestion--Leaves before being swallowed, moistened with a fluid of +the nature of the pancreatic secretion--Extra-stomachal digestion-- +Calciferous glands, structure of--Calcareous concretions formed in +the anterior pair of glands--The calcareous matter primarily an +excretion, but secondarily serves to neutralise the acids generated +during the digestive process. + + +Earth-worms are distributed throughout the world under the form of +a few genera, which externally are closely similar to one another. +The British species of Lumbricus have never been carefully +monographed; but we may judge of their probable number from those +inhabiting neighbouring countries. In Scandinavia there are eight +species, according to Eisen; {7} but two of these rarely burrow in +the ground, and one inhabits very wet places or even lives under +the water. We are here concerned only with the kinds which bring +up earth to the surface in the form of castings. Hoffmeister says +that the species in Germany are not well known, but gives the same +number as Eisen, together with some strongly marked varieties. {8} + +Earth-worms abound in England in many different stations. Their +castings may be seen in extraordinary numbers on commons and chalk- +downs, so as almost to cover the whole surface, where the soil is +poor and the grass short and thin. But they are almost or quite as +numerous in some of the London parks, where the grass grows well +and the soil appears rich. Even on the same field worms are much +more frequent in some places than in others, without any visible +difference in the nature of the soil. They abound in paved court- +yards close to houses; and an instance will be given in which they +had burrowed through the floor of a very damp cellar. I have seen +worms in black peat in a boggy field; but they are extremely rare, +or quite absent in the drier, brown, fibrous peat, which is so much +valued by gardeners. On dry, sandy or gravelly tracks, where heath +with some gorse, ferns, coarse grass, moss and lichens alone grow, +hardly any worms can be found. But in many parts of England, +wherever a path crosses a heath, its surface becomes covered with a +fine short sward. Whether this change of vegetation is due to the +taller plants being killed by the occasional trampling of man and +animals, or to the soil being occasionally manured by the droppings +from animals, I do not know. {9} On such grassy paths worm- +castings may often be seen. On a heath in Surrey, which was +carefully examined, there were only a few castings on these paths, +where they were much inclined; but on the more level parts, where a +bed of fine earth had been washed down from the steeper parts and +had accumulated to a thickness of a few inches, worm-castings +abounded. These spots seemed to be overstocked with worms, so that +they had been compelled to spread to a distance of a few feet from +the grassy paths, and here their castings had been thrown up among +the heath; but beyond this limit, not a single casting could be +found. A layer, though a thin one, of fine earth, which probably +long retains some moisture, is in all cases, as I believe, +necessary for their existence; and the mere compression of the soil +appears to be in some degree favourable to them, for they often +abound in old gravel walks, and in foot-paths across fields. + +Beneath large trees few castings can be found during certain +seasons of the year, and this is apparently due to the moisture +having been sucked out of the ground by the innumerable roots of +the trees; for such places may be seen covered with castings after +the heavy autumnal rains. Although most coppices and woods support +many worms, yet in a forest of tall and ancient beech-trees in +Knole Park, where the ground beneath was bare of all vegetation, +not a single casting could be found over wide spaces, even during +the autumn. Nevertheless, castings were abundant on some grass- +covered glades and indentations which penetrated this forest. On +the mountains of North Wales and on the Alps, worms, as I have been +informed, are in most places rare; and this may perhaps be due to +the close proximity of the subjacent rocks, into which worms cannot +burrow during the winter so as to escape being frozen. Dr. +McIntosh, however, found worm-castings at a height of 1500 feet on +Schiehallion in Scotland. They are numerous on some hills near +Turin at from 2000 to 3000 feet above the sea, and at a great +altitude on the Nilgiri Mountains in South India and on the +Himalaya. + +Earth-worms must be considered as terrestrial animals, though they +are still in one sense semi-aquatic, like the other members of the +great class of annelids to which they belong. M. Perrier found +that their exposure to the dry air of a room for only a single +night was fatal to them. On the other hand he kept several large +worms alive for nearly four months, completely submerged in water. +{10} During the summer when the ground is dry, they penetrate to a +considerable depth and cease to work, as they do during the winter +when the ground is frozen. Worms are nocturnal in their habits, +and at night may be seen crawling about in large numbers, but +usually with their tails still inserted in their burrows. By the +expansion of this part of their bodies, and with the help of the +short, slightly reflexed bristles, with which their bodies are +armed, they hold so fast that they can seldom be dragged out of the +ground without being torn into pieces. {11} During the day they +remain in their burrows, except at the pairing season, when those +which inhabit adjoining burrows expose the greater part of their +bodies for an hour or two in the early morning. Sick individuals, +which are generally affected by the parasitic larvae of a fly, must +also be excepted, as they wander about during the day and die on +the surface. After heavy rain succeeding dry weather, an +astonishing number of dead worms may sometimes be seen lying on the +ground. Mr. Galton informs me that on one such occasion (March, +1881), the dead worms averaged one for every two and a half paces +in length on a walk in Hyde Park, four paces in width. He counted +no less than 45 dead worms in one place in a length of sixteen +paces. From the facts above given, it is not probable that these +worms could have been drowned, and if they had been drowned they +would have perished in their burrows. I believe that they were +already sick, and that their deaths were merely hastened by the +ground being flooded. + +It has often been said that under ordinary circumstances healthy +worms never, or very rarely, completely leave their burrows at +night; but this is an error, as White of Selborne long ago knew. +In the morning, after there has been heavy rain, the film of mud or +of very fine sand over gravel-walks is often plainly marked with +their tracks. I have noticed this from August to May, both months +included, and it probably occurs during the two remaining months of +the year when they are wet. On these occasions, very few dead +worms could anywhere be seen. On January 31, 1881, after a long- +continued and unusually severe frost with much snow, as soon as a +thaw set in, the walks were marked with innumerable tracks. On one +occasion, five tracks were counted crossing a space of only an inch +square. They could sometimes be traced either to or from the +mouths of the burrows in the gravel-walks, for distances between 2 +or 3 up to 15 yards. I have never seen two tracks leading to the +same burrow; nor is it likely, from what we shall presently see of +their sense-organs, that a worm could find its way back to its +burrow after having once left it. They apparently leave their +burrows on a voyage of discovery, and thus they find new sites to +inhabit. + +Morren states {12} that worms often lie for hours almost motionless +close beneath the mouths of their burrows. I have occasionally +noticed the same fact with worms kept in pots in the house; so that +by looking down into their burrows, their heads could just be seen. +If the ejected earth or rubbish over the burrows be suddenly +removed, the end of the worm's body may very often be seen rapidly +retreating. This habit of lying near the surface leads to their +destruction to an immense extent. Every morning during certain +seasons of the year, the thrushes and blackbirds on all the lawns +throughout the country draw out of their holes an astonishing +number of worms, and this they could not do, unless they lay close +to the surface. It is not probable that worms behave in this +manner for the sake of breathing fresh air, for we have seen that +they can live for a long time under water. I believe that they lie +near the surface for the sake of warmth, especially in the morning; +and we shall hereafter find that they often coat the mouths of +their burrows with leaves, apparently to prevent their bodies from +coming into close contact with the cold damp earth. It is said +that they completely close their burrows during the winter. + +Structure.--A few remarks must be made on this subject. The body +of a large worm consists of from 100 to 200 almost cylindrical +rings or segments, each furnished with minute bristles. The +muscular system is well developed. Worms can crawl backwards as +well as forwards, and by the aid of their affixed tails can retreat +with extraordinary rapidity into their burrows. The mouth is +situated at the anterior end of the body, and is provided with a +little projection (lobe or lip, as it has been variously called) +which is used for prehension. Internally, behind the mouth, there +is a strong pharynx, shown in the accompanying diagram (Fig. 1) +which is pushed forwards when the animal eats, and this part +corresponds, according to Perrier, with the protrudable trunk or +proboscis of other annelids. The pharynx leads into the +oesophagus, on each side of which in the lower part there are three +pairs of large glands, which secrete a surprising amount of +carbonate of lime. These calciferous glands are highly remarkable, +for nothing like them is known in any other animal. Their use will +be discussed when we treat of the digestive process. In most of +the species, the oesophagus is enlarged into a crop in front of the +gizzard. This latter organ is lined with a smooth thick chitinous +membrane, and is surrounded by weak longitudinal, but powerful +transverse muscles. Perrier saw these muscles in energetic action; +and, as he remarks, the trituration of the food must be chiefly +effected by this organ, for worms possess no jaws or teeth of any +kind. Grains of sand and small stones, from the 1/20 to a little +more than the 1/10 inch in diameter, may generally be found in +their gizzards and intestines. As it is certain that worms swallow +many little stones, independently of those swallowed while +excavating their burrows, it is probable that they serve, like +mill-stones, to triturate their food. The gizzard opens into the +intestine, which runs in a straight course to the vent at the +posterior end of the body. The intestine presents a remarkable +structure, the typhlosolis, or, as the old anatomists called it, an +intestine within an intestine; and Claparede {13} has shown that +this consists of a deep longitudinal involution of the walls of the +intestine, by which means an extensive absorbent surface is gained. + +The circulatory system is well developed. Worms breathe by their +skin, as they do not possess any special respiratory organs. The +two sexes are united in the same individual, but two individuals +pair together. The nervous system is fairly well developed; and +the two almost confluent cerebral ganglia are situated very near to +the anterior end of the body. + +Senses.--Worms are destitute of eyes, and at first I thought that +they were quite insensible to light; for those kept in confinement +were repeatedly observed by the aid of a candle, and others out of +doors by the aid of a lantern, yet they were rarely alarmed, +although extremely timid animals. Other persons have found no +difficulty in observing worms at night by the same means. {14} + +Hoffmeister, however, states {15} that worms, with the exception of +a few individuals, are extremely sensitive to light; but he admits +that in most cases a certain time is requisite for its action. +These statements led me to watch on many successive nights worms +kept in pots, which were protected from currents of air by means of +glass plates. The pots were approached very gently, in order that +no vibration of the floor should be caused. When under these +circumstances worms were illuminated by a bull's-eye lantern having +slides of dark red and blue glass, which intercepted so much light +that they could be seen only with some difficulty, they were not at +all affected by this amount of light, however long they were +exposed to it. The light, as far as I could judge, was brighter +than that from the full moon. Its colour apparently made no +difference in the result. When they were illuminated by a candle, +or even by a bright paraffin lamp, they were not usually affected +at first. Nor were they when the light was alternately admitted +and shut off. Sometimes, however, they behaved very differently, +for as soon as the light fell on them, they withdrew into their +burrows with almost instantaneous rapidity. This occurred perhaps +once out of a dozen times. When they did not withdraw instantly, +they often raised the anterior tapering ends of their bodies from +the ground, as if their attention was aroused or as if surprise was +felt; or they moved their bodies from side to side as if feeling +for some object. They appeared distressed by the light; but I +doubt whether this was really the case, for on two occasions after +withdrawing slowly, they remained for a long time with their +anterior extremities protruding a little from the mouths of their +burrows, in which position they were ready for instant and complete +withdrawal. + +When the light from a candle was concentrated by means of a large +lens on the anterior extremity, they generally withdrew instantly; +but this concentrated light failed to act perhaps once out of half +a dozen trials. The light was on one occasion concentrated on a +worm lying beneath water in a saucer, and it instantly withdrew +into its burrow. In all cases the duration of the light, unless +extremely feeble, made a great difference in the result; for worms +left exposed before a paraffin lamp or a candle invariably +retreated into their burrows within from five to fifteen minutes; +and if in the evening the pots were illuminated before the worms +had come out of their burrows, they failed to appear. + +From the foregoing facts it is evident that light affects worms by +its intensity and by its duration. It is only the anterior +extremity of the body, where the cerebral ganglia lie, which is +affected by light, as Hoffmeister asserts, and as I observed on +many occasions. If this part is shaded, other parts of the body +may be fully illuminated, and no effect will be produced. As these +animals have no eyes, we must suppose that the light passes through +their skins, and in some manner excites their cerebral ganglia. It +appeared at first probable that the different manner in which they +were affected on different occasions might be explained, either by +the degree of extension of their skin and its consequent +transparency, or by some particular incident of the light; but I +could discover no such relation. One thing was manifest, namely, +that when worms were employed in dragging leaves into their burrows +or in eating them, and even during the short intervals whilst they +rested from their work, they either did not perceive the light or +were regardless of it; and this occurred even when the light was +concentrated on them through a large lens. So, again, whilst they +are paired, they will remain for an hour or two out of their +burrows, fully exposed to the morning light; but it appears from +what Hoffmeister says that a light will occasionally cause paired +individuals to separate. + +When a worm is suddenly illuminated and dashes like a rabbit into +its burrow--to use the expression employed by a friend--we are at +first led to look at the action as a reflex one. The irritation of +the cerebral ganglia appears to cause certain muscles to contract +in an inevitable manner, independently of the will or consciousness +of the animal, as if it were an automaton. But the different +effect which a light produced on different occasions, and +especially the fact that a worm when in any way employed and in the +intervals of such employment, whatever set of muscles and ganglia +may then have been brought into play, is often regardless of light, +are opposed to the view of the sudden withdrawal being a simple +reflex action. With the higher animals, when close attention to +some object leads to the disregard of the impressions which other +objects must be producing on them, we attribute this to their +attention being then absorbed; and attention implies the presence +of a mind. Every sportsman knows that he can approach animals +whilst they are grazing, fighting or courting, much more easily +than at other times. The state, also, of the nervous system of the +higher animals differs much at different times, for instance, a +horse is much more readily startled at one time than at another. +The comparison here implied between the actions of one of the +higher animals and of one so low in the scale as an earth-worm, may +appear far-fetched; for we thus attribute to the worm attention and +some mental power, nevertheless I can see no reason to doubt the +justice of the comparison. + +Although worms cannot be said to possess the power of vision, their +sensitiveness to light enables them to distinguish between day and +night; and they thus escape extreme danger from the many diurnal +animals which prey on them. Their withdrawal into their burrows +during the day appears, however, to have become an habitual action; +for worms kept in pots covered by glass plates, over which sheets +of black paper were spread, and placed before a north-east window, +remained during the day-time in their burrows and came out every +night; and they continued thus to act for a week. No doubt a +little light may have entered between the sheets of glass and the +blackened paper; but we know from the trials with coloured glass, +that worms are indifferent to a small amount of light. + +Worms appear to be less sensitive to moderate radiant heat than to +a bright light. I judge of this from having held at different +times a poker heated to dull redness near some worms, at a distance +which caused a very sensible degree of warmth in my hand. One of +them took no notice; a second withdrew into its burrow, but not +quickly; the third and fourth much more quickly, and the fifth as +quickly as possible. The light from a candle, concentrated by a +lens and passing through a sheet of glass which would intercept +most of the heat-rays, generally caused a much more rapid retreat +than did the heated poker. Worms are sensitive to a low +temperature, as may be inferred from their not coming out of their +burrows during a frost. + +Worms do not possess any sense of hearing. They took not the least +notice of the shrill notes from a metal whistle, which was +repeatedly sounded near them; nor did they of the deepest and +loudest tones of a bassoon. They were indifferent to shouts, if +care was taken that the breath did not strike them. When placed on +a table close to the keys of a piano, which was played as loudly as +possible, they remained perfectly quiet. + +Although they are indifferent to undulations in the air audible by +us, they are extremely sensitive to vibrations in any solid object. +When the pots containing two worms which had remained quite +indifferent to the sound of the piano, were placed on this +instrument, and the note C in the bass clef was struck, both +instantly retreated into their burrows. After a time they emerged, +and when G above the line in the treble clef was struck they again +retreated. Under similar circumstances on another night one worm +dashed into its burrow on a very high note being struck only once, +and the other worm when C in the treble clef was struck. On these +occasions the worms were not touching the sides of the pots, which +stood in saucers; so that the vibrations, before reaching their +bodies, had to pass from the sounding board of the piano, through +the saucer, the bottom of the pot and the damp, not very compact +earth on which they lay with their tails in their burrows. They +often showed their sensitiveness when the pot in which they lived, +or the table on which the pot stood, was accidentally and lightly +struck; but they appeared less sensitive to such jars than to the +vibrations of the piano; and their sensitiveness to jars varied +much at different times. + +It has often been said that if the ground is beaten or otherwise +made to tremble, worms believe that they are pursued by a mole and +leave their burrows. From one account that I have received, I have +no doubt that this is often the case; but a gentleman informs me +that he lately saw eight or ten worms leave their burrows and crawl +about the grass on some boggy land on which two men had just +trampled while setting a trap; and this occurred in a part of +Ireland where there were no moles. I have been assured by a +Volunteer that he has often seen many large earth-worms crawling +quickly about the grass, a few minutes after his company had fired +a volley with blank cartridges. The Peewit (Tringa vanellus, +Linn.) seems to know instinctively that worms will emerge if the +ground is made to tremble; for Bishop Stanley states (as I hear +from Mr. Moorhouse) that a young peewit kept in confinement used to +stand on one leg and beat the turf with the other leg until the +worms crawled out of their burrows, when they were instantly +devoured. Nevertheless, worms do not invariably leave their +burrows when the ground is made to tremble, as I know by having +beaten it with a spade, but perhaps it was beaten too violently. + +The whole body of a worm is sensitive to contact. A slight puff of +air from the mouth causes an instant retreat. The glass plates +placed over the pots did not fit closely, and blowing through the +very narrow chinks thus left, often sufficed to cause a rapid +retreat. They sometimes perceived the eddies in the air caused by +quickly removing the glass plates. When a worm first comes out of +its burrow, it generally moves the much extended anterior extremity +of its body from side to side in all directions, apparently as an +organ of touch; and there is some reason to believe, as we shall +see in the next chapter, that they are thus enabled to gain a +general notion of the form of an object. Of all their senses that +of touch, including in this term the perception of a vibration, +seems much the most highly developed. + +In worms the sense of smell apparently is confined to the +perception of certain odours, and is feeble. They were quite +indifferent to my breath, as long as I breathed on them very +gently. This was tried, because it appeared possible that they +might thus be warned of the approach of an enemy. They exhibited +the same indifference to my breath whilst I chewed some tobacco, +and while a pellet of cotton-wool with a few drops of millefleurs +perfume or of acetic acid was kept in my mouth. Pellets of cotton- +wool soaked in tobacco juice, in millefleurs perfume, and in +paraffin, were held with pincers and were waved about within two or +three inches of several worms, but they took no notice. On one or +two occasions, however, when acetic acid had been placed on the +pellets, the worms appeared a little uneasy, and this was probably +due to the irritation of their skins. The perception of such +unnatural odours would be of no service to worms; and as such timid +creatures would almost certainly exhibit some signs of any new +impression, we may conclude that they did not perceive these +odours. + +The result was different when cabbage-leaves and pieces of onion +were employed, both of which are devoured with much relish by +worms. Small square pieces of fresh and half-decayed cabbage- +leaves and of onion bulbs were on nine occasions buried in my pots, +beneath about 0.25 of an inch of common garden soil; and they were +always discovered by the worms. One bit of cabbage was discovered +and removed in the course of two hours; three were removed by the +next morning, that is, after a single night; two others after two +nights; and the seventh bit after three nights. Two pieces of +onion were discovered and removed after three nights. Bits of +fresh raw meat, of which worms are very fond, were buried, and were +not discovered within forty-eight hours, during which time they had +not become putrid. The earth above the various buried objects was +generally pressed down only slightly, so as not to prevent the +emission of any odour. On two occasions, however, the surface was +well watered, and was thus rendered somewhat compact. After the +bits of cabbage and onion had been removed, I looked beneath them +to see whether the worms had accidentally come up from below, but +there was no sign of a burrow; and twice the buried objects were +laid on pieces of tin-foil which were not in the least displaced. +It is of course possible that the worms whilst moving about on the +surface of the ground, with their tails affixed within their +burrows, may have poked their heads into the places where the above +objects were buried; but I have never seen worms acting in this +manner. Some pieces of cabbage-leaf and of onion were twice buried +beneath very fine ferruginous sand, which was slightly pressed down +and well watered, so as to be rendered very compact, and these +pieces were never discovered. On a third occasion the same kind of +sand was neither pressed down nor watered, and the pieces of +cabbage were discovered and removed after the second night. These +several facts indicate that worms possess some power of smell; and +that they discover by this means odoriferous and much-coveted kinds +of food. + +It may be presumed that all animals which feed on various +substances possess the sense of taste, and this is certainly the +case with worms. Cabbage-leaves are much liked by worms; and it +appears that they can distinguish between different varieties; but +this may perhaps be owing to differences in their texture. On +eleven occasions pieces of the fresh leaves of a common green +variety and of the red variety used for pickling were given them, +and they preferred the green, the red being either wholly neglected +or much less gnawed. On two other occasions, however, they seemed +to prefer the red. Half-decayed leaves of the red variety and +fresh leaves of the green were attacked about equally. When leaves +of the cabbage, horse-radish (a favourite food) and of the onion +were given together, the latter were always, and manifestly +preferred. Leaves of the cabbage, lime-tree, Ampelopsis, parsnip +(Pastinaca), and celery (Apium) were likewise given together; and +those of the celery were first eaten. But when leaves of cabbage, +turnip, beet, celery, wild cherry and carrots were given together, +the two latter kinds, especially those of the carrot, were +preferred to all the others, including those of celery. It was +also manifest after many trials that wild cherry leaves were +greatly preferred to those of the lime-tree and hazel (Corylus). +According to Mr. Bridgman the half-decayed leaves of Phlox verna +are particularly liked by worms. {16} + +Pieces of the leaves of cabbage, turnip, horse-radish and onion +were left on the pots during 22 days, and were all attacked and had +to be renewed; but during the whole of this time leaves of an +Artemisia and of the culinary sage, thyme and mint, mingled with +the above leaves, were quite neglected excepting those of the mint, +which were occasionally and very slightly nibbled. These latter +four kinds of leaves do not differ in texture in a manner which +could make them disagreeable to worms; they all have a strong +taste, but so have the four first mentioned kinds of leaves; and +the wide difference in the result must be attributed to a +preference by the worms for one taste over another. + +Mental Qualities.--There is little to be said on this head. We +have seen that worms are timid. It may be doubted whether they +suffer as much pain when injured, as they seem to express by their +contortions. Judging by their eagerness for certain kinds of food, +they must enjoy the pleasure of eating. Their sexual passion is +strong enough to overcome for a time their dread of light. They +perhaps have a trace of social feeling, for they are not disturbed +by crawling over each other's bodies, and they sometimes lie in +contact. According to Hoffmeister they pass the winter either +singly or rolled up with others into a ball at the bottom of their +burrows. {17} Although worms are so remarkably deficient in the +several sense-organs, this does not necessarily preclude +intelligence, as we know from such cases as those of Laura +Bridgman; and we have seen that when their attention is engaged, +they neglect impressions to which they would otherwise have +attended; and attention indicates the presence of a mind of some +kind. They are also much more easily excited at certain times than +at others. They perform a few actions instinctively, that is, all +the individuals, including the young, perform such actions in +nearly the same fashion. This is shown by the manner in which the +species of Perichaeta eject their castings, so as to construct +towers; also by the manner in which the burrows of the common +earth-worm are smoothly lined with fine earth and often with little +stones, and the mouths of their burrows with leaves. One of their +strongest instincts is the plugging up the mouths of their burrows +with various objects; and very young worms act in this manner. But +some degree of intelligence appears, as we shall see in the next +chapter, to be exhibited in this work,--a result which has +surprised me more than anything else in regard to worms. + +Food and Digestion.--Worms are omnivorous. They swallow an +enormous quantity of earth, out of which they extract any +digestible matter which it may contain; but to this subject I must +recur. They also consume a large number of half-decayed leaves of +all kinds, excepting a few which have an unpleasant taste or are +too tough for them; likewise petioles, peduncles, and decayed +flowers. But they will also consume fresh leaves, as I have found +by repeated trials. According to Morren {18} they will eat +particles of sugar and liquorice; and the worms which I kept drew +many bits of dry starch into their burrows, and a large bit had its +angles well rounded by the fluid poured out of their mouths. But +as they often drag particles of soft stone, such as of chalk, into +their burrows, I feel some doubt whether the starch was used as +food. Pieces of raw and roasted meat were fixed several times by +long pins to the surface of the soil in my pots, and night after +night the worms could be seen tugging at them, with the edges of +the pieces engulfed in their mouths, so that much was consumed. +Raw fat seems to be preferred even to raw meat or to any other +substance which was given them, and much was consumed. They are +cannibals, for the two halves of a dead worm placed in two of the +pots were dragged into the burrows and gnawed; but as far as I +could judge, they prefer fresh to putrid meat, and in so far I +differ from Hoffmeister. + +Leon Fredericq states {19} that the digestive fluid of worms is of +the same nature as the pancreatic secretion of the higher animals; +and this conclusion agrees perfectly with the kinds of food which +worms consume. Pancreatic juice emulsifies fat, and we have just +seen how greedily worms devour fat; it dissolves fibrin, and worms +eat raw meat; it converts starch into grape-sugar with wonderful +rapidity, and we shall presently show that the digestive fluid of +worms acts on starch. {20} But they live chiefly on half-decayed +leaves; and these would be useless to them unless they could digest +the cellulose forming the cell-walls; for it is well known that all +other nutritious substances are almost completely withdrawn from +leaves, shortly before they fall off. It has, however, now been +ascertained that some forms of cellulose, though very little or not +at all attacked by the gastric secretion of the higher animals, are +acted on by that from the pancreas. {21} + +The half-decayed or fresh leaves which worms intend to devour, are +dragged into the mouths of their burrows to a depth of from one to +three inches, and are then moistened with a secreted fluid. It has +been assumed that this fluid serves to hasten their decay; but a +large number of leaves were twice pulled out of the burrows of +worms and kept for many weeks in a very moist atmosphere under a +bell-glass in my study; and the parts which had been moistened by +the worms did not decay more quickly in any plain manner than the +other parts. When fresh leaves were given in the evening to worms +kept in confinement and examined early on the next morning, +therefore not many hours after they had been dragged into the +burrows, the fluid with which they were moistened, when tested with +neutral litmus paper, showed an alkaline reaction. This was +repeatedly found to be the case with celery, cabbage and turnip +leaves. Parts of the same leaves which had not been moistened by +the worms, were pounded with a few drops of distilled water, and +the juice thus extracted was not alkaline. Some leaves, however, +which had been drawn into burrows out of doors, at an unknown +antecedent period, were tried, and though still moist, they rarely +exhibited even a trace of alkaline reaction. + +The fluid, with which the leaves are bathed, acts on them whilst +they are fresh or nearly fresh, in a remarkable manner; for it +quickly kills and discolours them. Thus the ends of a fresh +carrot-leaf, which had been dragged into a burrow, were found after +twelve hours of a dark brown tint. Leaves of celery, turnip, +maple, elm, lime, thin leaves of ivy, and, occasionally those of +the cabbage were similarly acted on. The end of a leaf of Triticum +repens, still attached to a growing plant, had been drawn into a +burrow, and this part was dark brown and dead, whilst the rest of +the leaf was fresh and green. Several leaves of lime and elm +removed from burrows out of doors were found affected in different +degrees. The first change appears to be that the veins become of a +dull reddish-orange. The cells with chlorophyll next lose more or +less completely their green colour, and their contents finally +become brown. The parts thus affected often appeared almost black +by reflected light; but when viewed as a transparent object under +the microscope, minute specks of light were transmitted, and this +was not the case with the unaffected parts of the same leaves. +These effects, however, merely show that the secreted fluid is +highly injurious or poisonous to leaves; for nearly the same +effects were produced in from one to two days on various kinds of +young leaves, not only by artificial pancreatic fluid, prepared +with or without thymol, but quickly by a solution of thymol by +itself. On one occasion leaves of Corylus were much discoloured by +being kept for eighteen hours in pancreatic fluid, without any +thymol. With young and tender leaves immersion in human saliva +during rather warm weather, acted in the same manner as the +pancreatic fluid, but not so quickly. The leaves in all these +cases often became infiltrated with the fluid. + +Large leaves from an ivy plant growing on a wall were so tough that +they could not be gnawed by worms, but after four days they were +affected in a peculiar manner by the secretion poured out of their +mouths. The upper surfaces of the leaves, over which the worms had +crawled, as was shown by the dirt left on them, were marked in +sinuous lines, by either a continuous or broken chain of whitish +and often star-shaped dots, about 2 mm. in diameter. The +appearance thus presented was curiously like that of a leaf, into +which the larva of some minute insect had burrowed. But my son +Francis, after making and examining sections, could nowhere find +that the cell-walls had been broken down or that the epidermis had +been penetrated. When the section passed through the whitish dots, +the grains of chlorophyll were seen to be more or less discoloured, +and some of the palisade and mesophyll cells contained nothing but +broken down granular matter. These effects must be attributed to +the transudation of the secretion through the epidermis into the +cells. + +The secretion with which worms moisten leaves likewise acts on the +starch-granules within the cells. My son examined some leaves of +the ash and many of the lime, which had fallen off the trees and +had been partly dragged into worm-burrows. It is known that with +fallen leaves the starch-grains are preserved in the guard-cells of +the stomata. Now in several cases the starch had partially or +wholly disappeared from these cells, in the parts which had been +moistened by the secretion; while it was still well preserved in +the other parts of the same leaves. Sometimes the starch was +dissolved out of only one of the two guard-cells. The nucleus in +one case had disappeared, together with the starch-granules. The +mere burying of lime-leaves in damp earth for nine days did not +cause the destruction of the starch-granules. On the other hand, +the immersion of fresh lime and cherry leaves for eighteen hours in +artificial pancreatic fluid, led to the dissolution of the starch- +granules in the guard-cells as well as in the other cells. + +From the secretion with which the leaves are moistened being +alkaline, and from its acting both on the starch-granules and on +the protoplasmic contents of the cells, we may infer that it +resembles in nature not saliva, {22} but pancreatic secretion; and +we know from Fredericq that a secretion of this kind is found in +the intestines of worms. As the leaves which are dragged into the +burrows are often dry and shrivelled, it is indispensable for their +disintegration by the unarmed mouths of worms that they should +first be moistened and softened; and fresh leaves, however soft and +tender they may be, are similarly treated, probably from habit. +The result is that they are partially digested before they are +taken into the alimentary canal. I am not aware of any other case +of extra-stomachal digestion having been recorded. The boa- +constrictor is said to bathe its prey with saliva, but this is +doubtful; and it is done solely for the sake of lubricating its +prey. Perhaps the nearest analogy may be found in such plants as +Drosera and Dionaea; for here animal matter is digested and +converted into peptone not within a stomach, but on the surfaces of +the leaves. + +Calciferous Glands.--These glands (see Fig. 1), judging from their +size and from their rich supply of blood-vessels, must be of much +importance to the animal. But almost as many theories have been +advanced on their use as there have been observers. They consist +of three pairs, which in the common earth-worm debouch into the +alimentary canal in advance of the gizzard, but posteriorly to it +in Urochaeta and some other genera. {23} The two posterior pairs +are formed by lamellae, which, according to Claparede, are +diverticula from the oesophagus. {24} These lamellae are coated +with a pulpy cellular layer, with the outer cells lying free in +infinite numbers. If one of these glands is punctured and +squeezed, a quantity of white pulpy matter exudes, consisting of +these free cells. They are minute, and vary in diameter from 2 to +6 microns. They contain in their centres a little excessively fine +granular matter; but they look so like oil globules that Claparede +and others at first treated them with ether. This produces no +effect; but they are quickly dissolved with effervescence in acetic +acid, and when oxalate of ammonia is added to the solution a white +precipitate is thrown down. We may therefore conclude that they +contain carbonate of lime. If the cells are immersed in a very +little acid, they become more transparent, look like ghosts, and +are soon lost to view; but if much acid is added, they disappear +instantly. After a very large number have been dissolved, a +flocculent residue is left, which apparently consists of the +delicate ruptured cell-walls. In the two posterior pairs of glands +the carbonate of lime contained in the cells occasionally +aggregates into small rhombic crystals or into concretions, which +lie between the lamellae; but I have seen only one case, and +Claparede only a very few such cases. + +The two anterior glands differ a little in shape from the four +posterior ones, by being more oval. They differ also conspicuously +in generally containing several small, or two or three larger, or a +single very large concretion of carbonate of lime, as much as 1.5 +mm. in diameter. When a gland includes only a few very small +concretions, or, as sometimes happens, none at all, it is easily +overlooked. The large concretions are round or oval, and +exteriorly almost smooth. One was found which filled up not only +the whole gland, as is often the case, but its neck; so that it +resembled an olive-oil flask in shape. These concretions when +broken are seen to be more or less crystalline in structure. How +they escape from the gland is a marvel; but that they do escape is +certain, for they are often found in the gizzard, intestines, and +in the castings of worms, both with those kept in confinement and +those in a state of nature. + +Claparede says very little about the structure of the two anterior +glands, and he supposes that the calcareous matter of which the +concretions are formed is derived from the four posterior glands. +But if an anterior gland which contains only small concretions is +placed in acetic acid and afterwards dissected, or if sections are +made of such a gland without being treated with acid, lamellae like +those in the posterior glands and coated with cellular matter could +be plainly seen, together with a multitude of free calciferous +cells readily soluble in acetic acid. When a gland is completely +filled with a single large concretion, there are no free cells, as +these have been all consumed in forming the concretion. But if +such a concretion, or one of only moderately large size, is +dissolved in acid, much membranous matter is left, which appears to +consist of the remains of the formerly active lamellae. After the +formation and expulsion of a large concretion, new lamellae must be +developed in some manner. In one section made by my son, the +process had apparently commenced, although the gland contained two +rather large concretions, for near the walls several cylindrical +and oval pipes were intersected, which were lined with cellular +matter and were quite filled with free calciferous cells. A great +enlargement in one direction of several oval pipes would give rise +to the lamellae. + +Besides the free calciferous cells in which no nucleus was visible, +other and rather larger free cells were seen on three occasions; +and these contained a distinct nucleus and nucleolus. They were +only so far acted on by acetic acid that the nucleus was thus +rendered more distinct. A very small concretion was removed from +between two of the lamellae within an anterior gland. It was +imbedded in pulpy cellular matter, with many free calciferous +cells, together with a multitude of the larger, free, nucleated +cells, and these latter cells were not acted on by acetic acid, +while the former were dissolved. From this and other such cases I +am led to suspect that the calciferous cells are developed from the +larger nucleated ones; but how this was effected was not +ascertained. + +When an anterior gland contains several minute concretions, some of +these are generally angular or crystalline in outline, while the +greater number are rounded with an irregular mulberry-like surface. +Calciferous cells adhered to many parts of these mulberry-like +masses, and their gradual disappearance could be traced while they +still remained attached. It was thus evident that the concretions +are formed from the lime contained within the free calciferous +cells. As the smaller concretions increase in size, they come into +contact and unite, thus enclosing the now functionless lamellae; +and by such steps the formation of the largest concretions could be +followed. Why the process regularly takes place in the two +anterior glands, and only rarely in the four posterior glands, is +quite unknown. Morren says that these glands disappear during the +winter; and I have seen some instances of this fact, and others in +which either the anterior or posterior glands were at this season +so shrunk and empty, that they could be distinguished only with +much difficulty. + +With respect to the function of the calciferous glands, it is +probable that they primarily serve as organs of excretion, and +secondarily as an aid to digestion. Worms consume many fallen +leaves; and it is known that lime goes on accumulating in leaves +until they drop off the parent-plant, instead of being re-absorbed +into the stem or roots, like various other organic and inorganic +substances. {25} The ashes of a leaf of an acacia have been known +to contain as much as 72 per cent. of lime. Worms therefore would +be liable to become charged with this earth, unless there were some +special means for its excretion; and the calciferous glands are +well adapted for this purpose. The worms which live in mould close +over the chalk, often have their intestines filled with this +substance, and their castings are almost white. Here it is evident +that the supply of calcareous matter must be super-abundant. +Nevertheless with several worms collected on such a site, the +calciferous glands contained as many free calciferous cells, and +fully as many and large concretions, as did the glands of worms +which lived where there was little or no lime; and this indicates +that the lime is an excretion, and not a secretion poured into the +alimentary canal for some special purpose. + +On the other hand, the following considerations render it highly +probable that the carbonate of lime, which is excreted by the +glands, aids the digestive process under ordinary circumstances. +Leaves during their decay generate an abundance of various kinds of +acids, which have been grouped together under the term of humus +acids. We shall have to recur to this subject in our fifth +chapter, and I need here only say that these acids act strongly on +carbonate of lime. The half-decayed leaves which are swallowed in +such large quantities by worms would, therefore, after they have +been moistened and triturated in the alimentary canal, be apt to +produce such acids. And in the case of several worms, the contents +of the alimentary canal were found to be plainly acid, as shown by +litmus paper. This acidity cannot be attributed to the nature of +the digestive fluid, for pancreatic fluid is alkaline; and we have +seen that the secretion which is poured out of the mouths of worms +for the sake of preparing the leaves for consumption, is likewise +alkaline. The acidity can hardly be due to uric acid, as the +contents of the upper part of the intestine were often acid. In +one case the contents of the gizzard were slightly acid, those of +the upper intestines being more plainly acid. In another case the +contents of the pharynx were not acid, those of the gizzard +doubtfully so, while those of the intestine were distinctly acid at +a distance of 5 cm. below the gizzard. Even with the higher +herbivorous and omnivorous animals, the contents of the large +intestine are acid. "This, however, is not caused by any acid +secretion from the mucous membrane; the reaction of the intestinal +walls in the larger as in the small intestine is alkaline. It must +therefore arise from acid fermentations going on in the contents +themselves . . . In Carnivora the contents of the coecum are said +to be alkaline, and naturally the amount of fermentation will +depend largely on the nature of the food." {26} + +With worms not only the contents of the intestines, but their +ejected matter or the castings, are generally acid. Thirty +castings from different places were tested, and with three or four +exceptions were found to be acid; and the exceptions may have been +due to such castings not having been recently ejected; for some +which were at first acid, were on the following morning, after +being dried and again moistened, no longer acid; and this probably +resulted from the humus acids being, as is known to be the case, +easily decomposed. Five fresh castings from worms which lived in +mould close over the chalk, were of a whitish colour and abounded +with calcareous matter; and these were not in the least acid. This +shows how effectually carbonate of lime neutralises the intestinal +acids. When worms were kept in pots filled with fine ferruginous +sand, it was manifest that the oxide of iron, with which the grains +of silex were coated, had been dissolved and removed from them in +the castings. + +The digestive fluid of worms resembles in its action, as already +stated, the pancreatic secretion of the higher animals; and in +these latter, "pancreatic digestion is essentially alkaline; the +action will not take place unless some alkali be present; and the +activity of an alkaline juice is arrested by acidification, and +hindered by neutralization." {27} Therefore it seems highly +probable that the innumerable calciferous cells, which are poured +from the four posterior glands into the alimentary canal of worms, +serve to neutralise more or less completely the acids there +generated by the half-decayed leaves. We have seen that these +cells are instantly dissolved by a small quantity of acetic acid, +and as they do not always suffice to neutralise the contents of +even the upper part of the alimentary canal, the lime is perhaps +aggregated into concretions in the anterior pair of glands, in +order that some may be carried down to the posterior parts of the +intestine, where these concretions would be rolled about amongst +the acid contents. The concretions found in the intestines and in +the castings often have a worn appearance, but whether this is due +to some amount of attrition or of chemical corrosion could not be +told. Claparede believes that they are formed for the sake of +acting as mill-stones, and of thus aiding in the trituration of the +food. They may give some aid in this way; but I fully agree with +Perrier that this must be of quite subordinate importance, seeing +that the object is already attained by stones being generally +present in the gizzards and intestines of worms. + + + +CHAPTER II--HABITS OF WORMS--continued. + + + +Manner in which worms seize objects--Their power of suction--The +instinct of plugging up the mouths of their burrows--Stones piled +over the burrows--The advantages thus gained--Intelligence shown by +worms in their manner of plugging up their burrows--Various kinds +of leaves and other objects thus used--Triangles of paper--Summary +of reasons for believing that worms exhibit some intelligence-- +Means by which they excavate their burrows, by pushing away the +earth and swallowing it--Earth also swallowed for the nutritious +matter which it contains--Depth to which worms burrow, and the +construction of their burrows--Burrows lined with castings, and in +the upper part with leaves--The lowest part paved with little +stones or seeds--Manner in which the castings are ejected--The +collapse of old burrows--Distribution of worms--Tower-like castings +in Bengal--Gigantic castings on the Nilgiri Mountains--Castings +ejected in all countries. + + +In the pots in which worms were kept, leaves were pinned down to +the soil, and at night the manner in which they were seized could +be observed. The worms always endeavoured to drag the leaves +towards their burrows; and they tore or sucked off small fragments, +whenever the leaves were sufficiently tender. They generally +seized the thin edge of a leaf with their mouths, between the +projecting upper and lower lip; the thick and strong pharynx being +at the same time, as Perrier remarks, pushed forward within their +bodies, so as to afford a point of resistance for the upper lip. +In the case of broad flat objects they acted in a wholly different +manner. The pointed anterior extremity of the body, after being +brought into contact with an object of this kind, was drawn within +the adjoining rings, so that it appeared truncated and became as +thick as the rest of the body. This part could then be seen to +swell a little; and this, I believe, is due to the pharynx being +pushed a little forwards. Then by a slight withdrawal of the +pharynx or by its expansion, a vacuum was produced beneath the +truncated slimy end of the body whilst in contact with the object; +and by this means the two adhered firmly together. {28} That under +these circumstances a vacuum was produced was plainly seen on one +occasion, when a large worm lying beneath a flaccid cabbage leaf +tried to drag it away; for the surface of the leaf directly over +the end of the worm's body became deeply pitted. On another +occasion a worm suddenly lost its hold on a flat leaf; and the +anterior end of the body was momentarily seen to be cup-formed. +Worms can attach themselves to an object beneath water in the same +manner; and I saw one thus dragging away a submerged slice of an +onion-bulb. + +The edges of fresh or nearly fresh leaves affixed to the ground +were often nibbled by the worms; and sometimes the epidermis and +all the parenchyma on one side was gnawed completely away over a +considerable space; the epidermis alone on the opposite side being +left quite clean. The veins were never touched, and leaves were +thus sometimes partly converted into skeletons. As worms have no +teeth and as their mouths consist of very soft tissue, it may be +presumed that they consume by means of suction the edges and the +parenchyma of fresh leaves, after they have been softened by the +digestive fluid. They cannot attack such strong leaves as those of +sea-kale or large and thick leaves of ivy; though one of the latter +after it had become rotten was reduced in parts to the state of a +skeleton. + +Worms seize leaves and other objects, not only to serve as food, +but for plugging up the mouths of their burrows; and this is one of +their strongest instincts. They sometimes work so energetically +that Mr. D. F. Simpson, who has a small walled garden where worms +abound in Bayswater, informs me that on a calm damp evening he +there heard so extraordinary a rustling noise from under a tree +from which many leaves had fallen, that he went out with a light +and discovered that the noise was caused by many worms dragging the +dry leaves and squeezing them into the burrows. Not only leaves, +but petioles of many kinds, some flower-peduncles, often decayed +twigs of trees, bits of paper, feathers, tufts of wool and horse- +hairs are dragged into their burrows for this purpose. I have seen +as many as seventeen petioles of a Clematis projecting from the +mouth of one burrow, and ten from the mouth of another. Some of +these objects, such as the petioles just named, feathers, &c., are +never gnawed by worms. In a gravel-walk in my garden I found many +hundred leaves of a pine-tree (P. austriaca or nigricans) drawn by +their bases into burrows. The surfaces by which these leaves are +articulated to the branches are shaped in as peculiar a manner as +is the joint between the leg-bones of a quadruped; and if these +surfaces had been in the least gnawed, the fact would have been +immediately visible, but there was no trace of gnawing. Of +ordinary dicotyledonous leaves, all those which are dragged into +burrows are not gnawed. I have seen as many as nine leaves of the +lime-tree drawn into the same burrow, and not nearly all of them +had been gnawed; but such leaves may serve as a store for future +consumption. Where fallen leaves are abundant, many more are +sometimes collected over the mouth of a burrow than can be used, so +that a small pile of unused leaves is left like a roof over those +which have been partly dragged in. + +A leaf in being dragged a little way into a cylindrical burrow is +necessarily much folded or crumpled. When another leaf is drawn +in, this is done exteriorly to the first one, and so on with the +succeeding leaves; and finally all become closely folded and +pressed together. Sometimes the worm enlarges the mouth of its +burrow, or makes a fresh one close by, so as to draw in a still +larger number of leaves. They often or generally fill up the +interstices between the drawn-in leaves with moist viscid earth +ejected from their bodies; and thus the mouths of the burrows are +securely plugged. Hundreds of such plugged burrows may be seen in +many places, especially during the autumnal and early winter +months. But, as will hereafter be shown, leaves are dragged into +the burrows not only for plugging them up and for food, but for the +sake of lining the upper part or mouth. + +When worms cannot obtain leaves, petioles, sticks, &c., with which +to plug up the mouths of their burrows, they often protect them by +little heaps of stones; and such heaps of smooth rounded pebbles +may frequently be seen on gravel-walks. Here there can be no +question about food. A lady, who was interested in the habits of +worms, removed the little heaps of stones from the mouths of +several burrows and cleared the surface of the ground for some +inches all round. She went out on the following night with a +lantern, and saw the worms with their tails fixed in their burrows, +dragging the stones inwards by the aid of their mouths, no doubt by +suction. "After two nights some of the holes had 8 or 9 small +stones over them; after four nights one had about 30, and another +34 stones." {29} One stone--which had been dragged over the +gravel-walk to the mouth of a burrow weighed two ounces; and this +proves how strong worms are. But they show greater strength in +sometimes displacing stones in a well-trodden gravel-walk; that +they do so, may be inferred from the cavities left by the displaced +stones being exactly filled by those lying over the mouths of +adjoining burrows, as I have myself observed. + +Work of this kind is usually performed during the night; but I have +occasionally known objects to be drawn into the burrows during the +day. What advantage the worms derive from plugging up the mouths +of their burrows with leaves, &c., or from piling stones over them, +is doubtful. They do not act in this manner at the times when they +eject much earth from their burrows; for their castings then serve +to cover the mouths. When gardeners wish to kill worms on a lawn, +it is necessary first to brush or rake away the castings from the +surface, in order that the lime-water may enter the burrows. {30} +It might be inferred from this fact that the mouths are plugged up +with leaves, &c., to prevent the entrance of water during heavy +rain; but it may be urged against this view that a few, loose, +well-rounded stones are ill-adapted to keep out water. I have +moreover seen many burrows in the perpendicularly cut turf-edgings +to gravel-walks, into which water could hardly flow, as well +plugged as burrows on a level surface. It is not probable that the +plugs or piles of stones serve to conceal the burrows from +scolopendras, which, according to Hoffmeister, {31} are the +bitterest enemies of worms, or from the larger species of Carabus +and Staphylinus which attack them ferociously, for these animals +are nocturnal, and the burrows are opened at night. May not worms +when the mouth of the burrow is protected be able to remain with +safety with their heads close to it, which we know that they like +to do, but which costs so many of them their lives? Or may not the +plugs check the free ingress of the lowest stratum of air, when +chilled by radiation at night, from the surrounding ground and +herbage? I am inclined to believe in this latter view: firstly, +because when worms were kept in pots in a room with a fire, in +which case cold air could not enter the burrows, they plugged them +up in a slovenly manner; and secondarily, because they often coat +the upper part of their burrows with leaves, apparently to prevent +their bodies from coming into close contact with the cold damp +earth. Mr. E. Parfitt has suggested to me that the mouths of the +burrows are closed in order that the air within them may be kept +thoroughly damp, and this seems the most probable explanation of +the habit. But the plugging-up process may serve for all the above +purposes. + +Whatever the motive may be, it appears that worms much dislike +leaving the mouths of their burrows open. Nevertheless they will +reopen them at night, whether or not they can afterwards close +them. Numerous open burrows may be seen on recently-dug ground, +for in this case the worms eject their castings in cavities left in +the ground, or in the old burrows instead of piling them over the +mouths of their burrows, and they cannot collect objects on the +surface by which the mouths might be protected. So again on a +recently disinterred pavement of a Roman villa at Abinger +(hereafter to be described) the worms pertinaciously opened their +burrows almost every night, when these had been closed by being +trampled on, although they were rarely able to find a few minute +stones wherewith to protect them. + +Intelligence shown by worms in their manner of plugging up their +burrows.--If a man had to plug up a small cylindrical hole, with +such objects as leaves, petioles or twigs, he would drag or push +them in by their pointed ends; but if these objects were very thin +relatively to the size of the hole, he would probably insert some +by their thicker or broader ends. The guide in his case would be +intelligence. It seemed therefore worth while to observe carefully +how worms dragged leaves into their burrows; whether by their tips +or bases or middle parts. It seemed more especially desirable to +do this in the case of plants not natives to our country; for +although the habit of dragging leaves into their burrows is +undoubtedly instinctive with worms, yet instinct could not tell +them how to act in the case of leaves about which their progenitors +knew nothing. If, moreover, worms acted solely through instinct or +an unvarying inherited impulse, they would draw all kinds of leaves +into their burrows in the same manner. If they have no such +definite instinct, we might expect that chance would determine +whether the tip, base or middle was seized. If both these +alternatives are excluded, intelligence alone is left; unless the +worm in each case first tries many different methods, and follows +that alone which proves possible or the most easy; but to act in +this manner and to try different methods makes a near approach to +intelligence. + +In the first place 227 withered leaves of various kinds, mostly of +English plants, were pulled out of worm-burrows in several places. +Of these, 181 had been drawn into the burrows by or near their +tips, so that the foot-stalk projected nearly upright from the +mouth of the burrow; 20 had been drawn in by their bases, and in +this case the tips projected from the burrows; and 26 had been +seized near the middle, so that these had been drawn in +transversely and were much crumpled. Therefore 80 per cent. +(always using the nearest whole number) had been drawn in by the +tip, 9 per cent. by the base or foot-stalk, and 11 per cent. +transversely or by the middle. This alone is almost sufficient to +show that chance does not determine the manner in which leaves are +dragged into the burrows. + +Of the above 227 leaves, 70 consisted of the fallen leaves of the +common lime-tree, which is almost certainly not a native of +England. These leaves are much acuminated towards the tip, and are +very broad at the base with a well-developed foot-stalk. They are +thin and quite flexible when half-withered. Of the 70, 79 per +cent. had been drawn in by or near the tip; 4 per cent. by or near +the base; and 17 per cent. transversely or by the middle. These +proportions agree very closely, as far as the tip is concerned, +with those before given. But the percentage drawn in by the base +is smaller, which may be attributed to the breadth of the basal +part of the blade. We here, also, see that the presence of a foot- +stalk, which it might have been expected would have tempted the +worms as a convenient handle, has little or no influence in +determining the manner in which lime leaves are dragged into the +burrows. The considerable proportion, viz., 17 per cent., drawn in +more or less transversely depends no doubt on the flexibility of +these half-decayed leaves. The fact of so many having been drawn +in by the middle, and of some few having been drawn in by the base, +renders it improbable that the worms first tried to draw in most of +the leaves by one or both of these methods, and that they +afterwards drew in 79 per cent. by their tips; for it is clear that +they would not have failed in drawing them in by the base or +middle. + +The leaves of a foreign plant were next searched for, the blades of +which were not more pointed towards the apex than towards the base. +This proved to be the case with those of a laburnum (a hybrid +between Cytisus alpinus and laburnum) for on doubling the terminal +over the basal half, they generally fitted exactly; and when there +was any difference, the basal half was a little the narrower. It +might, therefore, have been expected that an almost equal number of +these leaves would have been drawn in by the tip and base, or a +slight excess in favour of the latter. But of 73 leaves (not +included in the first lot of 227) pulled out of worm-burrows, 63 +per cent. had been drawn in by the tip; 27 per cent. by the base, +and 10 per cent. transversely. We here see that a far larger +proportion, viz., 27 per cent. were drawn in by the base than in +the case of lime leaves, the blades of which are very broad at the +base, and of which only 4 per cent. had thus been drawn in. We may +perhaps account for the fact of a still larger proportion of the +laburnum leaves not having been drawn in by the base, by worms +having acquired the habit of generally drawing in leaves by their +tips and thus avoiding the foot-stalk. For the basal margin of the +blade in many kinds of leaves forms a large angle with the foot- +stalk; and if such a leaf were drawn in by the foot-stalk, the +basal margin would come abruptly into contact with the ground on +each side of the burrow, and would render the drawing in of the +leaf very difficult. + +Nevertheless worms break through their habit of avoiding the foot- +stalk, if this part offers them the most convenient means for +drawing leaves into their burrows. The leaves of the endless +hybridised varieties of the Rhododendron vary much in shape; some +are narrowest towards the base and others towards the apex. After +they have fallen off, the blade on each side of the midrib often +becomes curled up while drying, sometimes along the whole length, +sometimes chiefly at the base, sometimes towards the apex. Out of +28 fallen leaves on one bed of peat in my garden, no less than 23 +were narrower in the basal quarter than in the terminal quarter of +their length; and this narrowness was chiefly due to the curling in +of the margins. Out of 36 fallen leaves on another bed, in which +different varieties of the Rhododendron grew, only 17 were narrower +towards the base than towards the apex. My son William, who first +called my attention to this case, picked up 237 fallen leaves in +his garden (where the Rhododendron grows in the natural soil) and +of these 65 per cent. could have been drawn by worms into their +burrows more easily by the base or foot-stalk than by the tip; and +this was partly due to the shape of the leaf and in a less degree +to the curling in of the margins: 27 per cent. could have been +drawn in more easily by the tip than by the base: and 8 per cent. +with about equal ease by either end. The shape of a fallen leaf +ought to be judged of before one end has been drawn into a burrow, +for after this has happened, the free end, whether it be the base +or apex, will dry more quickly than the end imbedded in the damp +ground; and the exposed margins of the free end will consequently +tend to become more curled inwards than they were when the leaf was +first seized by the worm. My son found 91 leaves which had been +dragged by worms into their burrows, though not to a great depth; +of these 66 per cent. had been drawn in by the base or foot-stalk; +and 34 per cent, by the tip. In this case, therefore, the worms +judged with a considerable degree of correctness how best to draw +the withered leaves of this foreign plant into their burrows; +notwithstanding that they had to depart from their usual habit of +avoiding the foot-stalk. + +On the gravel-walks in my garden a very large number of leaves of +three species of Pinus (P. austriaca, nigricans and sylvestris) are +regularly drawn into the mouths of worm burrows. These leaves +consist of two so-called needles, which are of considerable length +in the two first and short in the last named species, and are +united to a common base; and it is by this part that they are +almost invariably drawn into the burrows. I have seen only two or +at most three exceptions to this rule with worms in a state of +nature. As the sharply pointed needles diverge a little, and as +several leaves are drawn into the same burrow, each tuft forms a +perfect chevaux de frise. On two occasions many of these tufts +were pulled up in the evening, but by the following morning fresh +leaves had been pulled in, and the burrows were again well +protected. These leaves could not be dragged into the burrows to +any depth, except by their bases, as a worm cannot seize hold of +the two needles at the same time, and if one alone were seized by +the apex, the other would be pressed against the ground and would +resist the entry of the seized one. This was manifest in the above +mentioned two or three exceptional cases. In order, therefore, +that worms should do their work well, they must drag pine-leaves +into their burrows by their bases, where the two needles are +conjoined. But how they are guided in this work is a perplexing +question. + +This difficulty led my son Francis and myself to observe worms in +confinement during several nights by the aid of a dim light, while +they dragged the leaves of the above named pines into their +burrows. They moved the anterior extremities of their bodies about +the leaves, and on several occasions when they touched the sharp +end of a needle they withdrew suddenly as if pricked. But I doubt +whether they were hurt, for they are indifferent to very sharp +objects, and will swallow even rose-thorns and small splinters of +glass. It may also be doubted, whether the sharp ends of the +needles serve to tell them that this is the wrong end to seize; for +the points were cut off many leaves for a length of about one inch, +and fifty-seven of them thus treated were drawn into the burrows by +their bases, and not one by the cut-off ends. The worms in +confinement often seized the needles near the middle and drew them +towards the mouths of their burrows; and one worm tried in a +senseless manner to drag them into the burrow by bending them. +They sometimes collected many more leaves over the mouths of their +burrows (as in the case formerly mentioned of lime-leaves) than +could enter them. On other occasions, however, they behaved very +differently; for as soon as they touched the base of a pine-leaf, +this was seized, being sometimes completely engulfed in their +mouths, or a point very near the base was seized, and the leaf was +then quickly dragged or rather jerked into their burrows. It +appeared both to my son and myself as if the worms instantly +perceived as soon as they had seized a leaf in the proper manner. +Nine such cases were observed, but in one of them the worm failed +to drag the leaf into its burrow, as it was entangled by other +leaves lying near. In another case a leaf stood nearly upright +with the points of the needles partly inserted into a burrow, but +how placed there was not seen; and then the worm reared itself up +and seized the base, which was dragged into the mouth of the burrow +by bowing the whole leaf. On the other hand, after a worm had +seized the base of a leaf, this was on two occasions relinquished +from some unknown motive. + +As already remarked, the habit of plugging up the mouths of the +burrows with various objects, is no doubt instinctive in worms; and +a very young one, born in one of my pots, dragged for some little +distance a Scotch-fir leaf, one needle of which was as long and +almost as thick as its own body. No species of pine is endemic in +this part of England, it is therefore incredible that the proper +manner of dragging pine-leaves into the burrows can be instinctive +with our worms. But as the worms on which the above observations +were made, were dug up beneath or near some pines, which had been +planted there about forty years, it was desirable to prove that +their actions were not instinctive. Accordingly, pine-leaves were +scattered on the ground in places far removed from any pine-tree, +and 90 of them were drawn into the burrows by their bases. Only +two were drawn in by the tips of the needles, and these were not +real exceptions, as one was drawn in for a very short distance, and +the two needles of the other cohered. Other pine-leaves were given +to worms kept in pots in a warm room, and here the result was +different; for out of 42 leaves drawn into the burrows, no less +than i6 were drawn in by the tips of the needles. These worms, +however, worked in a careless or slovenly manner; for the leaves +were often drawn in to only a small depth; sometimes they were +merely heaped over the mouths of the burrows, and sometimes none +were drawn in. I believe that this carelessness may be accounted +for either by the warmth of the air, or by its dampness, as the +pots were covered by glass plates; the worms consequently did not +care about plugging up their holes effectually. Pots tenanted by +worms and covered with a net which allowed the free entrance of +air, were left out of doors for several nights, and now 72 leaves +were all properly drawn in by their bases. + +It might perhaps be inferred from the facts as yet given, that +worms somehow gain a general notion of the shape or structure of +pine-leaves, and perceive that it is necessary for them to seize +the base where the two needles are conjoined. But the following +cases make this more than doubtful. The tips of a large number of +needles of P. austriaca were cemented together with shell-lac +dissolved in alcohol, and were kept for some days, until, as I +believe, all odour or taste had been lost; and they were then +scattered on the ground where no pine-trees grew, near burrows from +which the plugging had been removed. Such leaves could have been +drawn into the burrows with equal ease by either end; and judging +from analogy and more especially from the case presently to be +given of the petioles of Clematis montana, I expected that the apex +would have been preferred. But the result was that out of 121 +leaves with the tips cemented, which were drawn into burrows, 108 +were drawn in by their bases, and only 13 by their tips. Thinking +that the worms might possibly perceive and dislike the smell or +taste of the shell-lac, though this was very improbable, especially +after the leaves had been left out during several nights, the tips +of the needles of many leaves were tied together with fine thread. +Of leaves thus treated 150 were drawn into burrows--123 by the base +and 27 by the tied tips; so that between four land five times as +many were drawn in by the base as by the tip. It is possible that +the short cut-off ends of the thread with which they were tied, may +have tempted the worms to drag in a larger proportional number by +the tips than when cement was used. Of the leaves with tied and +cemented tips taken together (271 in number) 85 per cent. were +drawn in by the base and 15 per cent. by the tips. We may +therefore infer that it is not the divergence of the two needles +which leads worms in a state of nature almost invariably to drag +pine-leaves into their burrows by the base. Nor can it be the +sharpness of the points of the needles which determines them; for, +as we have seen, many leaves with the points cut off were drawn in +by their bases. We are thus led to conclude, that with pine-leaves +there must be something attractive to worms in the base, +notwithstanding that few ordinary leaves are drawn in by the base +or foot-stalk. + +Petioles.--We will now turn to the petioles or foot-stalks of +compound leaves, after the leaflets have fallen off. Those from +Clematis montana, which grew over a verandah, were dragged early in +January in large numbers into the burrows on an adjoining gravel- +walk, lawn, and flower-bed. These petioles vary from 2.5 to 4.5 +inches in length, are rigid and of nearly uniform thickness, except +close to the base where they thicken rather abruptly, being here +about twice as thick as in any other part. The apex is somewhat +pointed, but soon withers and is then easily broken off. Of these +petioles, 314 were pulled out of burrows in the above specified +sites; and it was found that 76 per cent. had been drawn in by +their tips, and 24 per cent by their bases; so that those drawn in +by the tip were a little more than thrice as many as those drawn in +by the base. Some of those extracted from the well-beaten gravel- +walk were kept separate from the others; and of these (59 in +number) nearly five times as many had been drawn in by the tip as +by the base; whereas of those extracted from the lawn and flower- +bed, where from the soil yielding more easily, less care would be +necessary in plugging up the burrows, the proportion of those drawn +in by the tip (130) to those drawn in by the base (48) was rather +less than three to one. That these petioles had been dragged into +the burrows for plugging them up, and not for food, was manifest, +as neither end, as far as I could see, had been gnawed. As several +petioles are used to plug up the same burrow, in one case as many +as 10, and in another case as many as 15, the worms may perhaps at +first draw in a few by the thicker end so as to save labour; but +afterwards a large majority are drawn in by the pointed end, in +order to plug up the hole securely. + +The fallen petioles of our native ash-tree were next observed, and +the rule with most objects, viz., that a large majority are dragged +into the burrows by the more pointed end, had not here been +followed; and this fact much surprised me at first. These petioles +vary in length from 5 to 8.5 inches; they are thick and fleshy +towards the base, whence they taper gently towards the apex, which +is a little enlarged and truncated where the terminal leaflet had +been originally attached. Under some ash-trees growing in a grass- +field, 229 petioles were pulled out of worm burrows early in +January, and of these 51.5 per cent. had been drawn in by the base, +and 48.5 per cent. by the apex. This anomaly was however readily +explained as soon as the thick basal part was examined; for in 78 +out of 103 petioles, this part had been gnawed by worms, just above +the horse-shoe shaped articulation. In most cases there could be +no mistake about the gnawing; for ungnawed petioles which were +examined after being exposed to the weather for eight additional +weeks had not become more disintegrated or decayed near the base +than elsewhere. It is thus evident that the thick basal end of the +petiole is drawn in not solely for the sake of plugging up the +mouths of the burrows, but as food. Even the narrow truncated tips +of some few petioles had been gnawed; and this was the case in 6 +out of 37 which were examined for this purpose. Worms, after +having drawn in and gnawed the basal end, often push the petioles +out of their burrows; and then drag in fresh ones, either by the +base for food, or by the apex for plugging up the mouth more +effectually. Thus, out of 37 petioles inserted by their tips, 5 +had been previously drawn in by the base, for this part had been +gnawed. Again, I collected a handful of petioles lying loose on +the ground close to some plugged-up burrows, where the surface was +thickly strewed with other petioles which apparently had never been +touched by worms; and 14 out of 47 (i.e. nearly one-third), after +having had their bases gnawed had been pushed out of the burrows +and were now lying on the ground. From these several facts we may +conclude that worms draw in some petioles of the ash by the base to +serve as food, and others by the tip to plug up the mouths of their +burrows in the most efficient manner. + +The petioles of Robinia pseudo-acacia vary from 4 or 5 to nearly 12 +inches in length; they are thick close to the base before the +softer parts have rotted off, and taper much towards the upper end. +They are so flexible that I have seen some few doubled up and thus +drawn into the burrows of worms. Unfortunately these petioles were +not examined until February, by which time the softer parts had +completely rotted off, so that it was impossible to ascertain +whether worms had gnawed the bases, though this is in itself +probable. Out of 121 petioles extracted from burrows early in +February, 68 were imbedded by the base, and 53 by the apex. On +February 5 all the petioles which had been drawn into the burrows +beneath a Robinia, were pulled up; and after an interval of eleven +days, 35 petioles had been again dragged in, 19 by the base, and 16 +by the apex. Taking these two lots together, 56 per cent. were +drawn in by the base, and 44 per cent. by the apex. As all the +softer parts had long ago rotted off, we may feel sure, especially +in the latter case, that none had been drawn in as food. At this +season, therefore, worms drag these petioles into their burrows +indifferently by either end, a slight preference being given to the +base. This latter fact may be accounted for by the difficulty of +plugging up a burrow with objects so extremely thin as are the +upper ends. In support of this view, it may be stated that out of +the 16 petioles which had been drawn in by their upper ends, the +more attenuated terminal portion of 7 had been previously broken +off by some accident. + +Triangles of paper.--Elongated triangles were cut out of moderately +stiff writing-paper, which was rubbed with raw fat on both sides, +so as to prevent their becoming excessively limp when exposed at +night to rain and dew. The sides of all the triangles were three +inches in length, with the bases of 120 one inch, and of the other +183 half an inch in length. These latter triangles were very +narrow or much acuminated. {32} As a check on the observations +presently to be given, similar triangles in a damp state were +seized by a very narrow pair of pincers at different points and at +all inclinations with reference to the margins, and were then drawn +into a short tube of the diameter of a worm-burrow. If seized by +the apex, the triangle was drawn straight into the tube, with its +margins infolded; if seized at some little distance from the apex, +for instance at half an inch, this much was doubled back within the +tube. So it was with the base and basal angles, though in this +case the triangles offered, as might have been expected, much more +resistance to being drawn in. If seized near the middle the +triangle was doubled up, with the apex and base left sticking out +of the tube. As the sides of the triangles were three inches in +length, the result of their being drawn into a tube or into a +burrow in different ways, may be conveniently divided into three +groups: those drawn in by the apex or within an inch of it; those +drawn in by the base or within an inch of it; and those drawn in by +any point in the middle inch. + +In order to see how the triangles would be seized by worms, some in +a damp state were given to worms kept in confinement. They were +seized in three different manners in the case of both the narrow +and broad triangles: viz., by the margin; by one of the three +angles, which was often completely engulfed in their mouths; and +lastly, by suction applied to any part of the flat surface. If +lines parallel to the base and an inch apart, are drawn across a +triangle with the sides three inches in length, it will be divided +into three parts of equal length. Now if worms seized +indifferently by chance any part, they would assuredly seize on the +basal part or division far oftener than on either of the two other +divisions. For the area of the basal to the apical part is as 5 to +1, so that the chance of the former being drawn into a burrow by +suction, will be as 5 to 1, compared with the apical part. The +base offers two angles and the apex only one, so that the former +would have twice as good a chance (independently of the size of the +angles) of being engulfed in a worm's mouth, as would the apex. It +should, however, be stated that the apical angle is not often +seized by worms; the margin at a little distance on either side +being preferred. I judge of this from having found in 40 out of 46 +cases in which triangles had been drawn into burrows by their +apical ends, that the tip had been doubled back within the burrow +for a length of between 1/20 of an inch and 1 inch. Lastly, the +proportion between the margins of the basal and apical parts is as +3 to 2 for the broad, and 2.5 to 2 for the narrow triangles. From +these several considerations it might certainly have been expected, +supposing that worms seized hold of the triangles by chance, that a +considerably larger proportion would have been dragged into the +burrows by the basal than by the apical part; but we shall +immediately see how different was the result. + +Triangles of the above specified sizes were scattered on the ground +in many places and on many successive nights near worm-burrows, +from which the leaves, petioles, twigs, &c., with which they had +been plugged, were removed. Altogether 303 triangles were drawn by +worms into their burrows: 12 others were drawn in by both ends, +but as it was impossible to judge by which end they had been first +seized, these are excluded. Of the 303, 62 per cent. had been +drawn in by the apex (using this term for all drawn in by the +apical part, one inch in length); 15 per cent. by the middle; and +23 per cent. by the basal part. If they had been drawn +indifferently by any point, the proportion for the apical, middle +and basal parts would have been 33.3 per cent. for each; but, as we +have just seen, it might have been expected that a much larger +proportion would have been drawn in by the basal than by any other +part. As the case stands, nearly three times as many were drawn in +by the apex as by the base. If we consider the broad triangles by +themselves, 59 per cent. were drawn in by the apex, 25 per cent. by +the middle, and 16 per cent. by the base. Of the narrow triangles, +65 per cent. were drawn in by the apex, 14 per cent, by the middle, +and 21 per cent. by the base; so that here those drawn in by the +apex were more than 3 times as many as those drawn in by the base. +We may therefore conclude that the manner in which the triangles +are drawn into the burrows is not a matter of chance. + +In eight cases, two triangles had been drawn into the same burrow, +and in seven of these cases, one had been drawn in by the apex and +the other by the base. This again indicates that the result is not +determined by chance. Worms appear sometimes to revolve in the act +of drawing in the triangles, for five out of the whole lot had been +wound into an irregular spire round the inside of the burrow. +Worms kept in a warm room drew 63 triangles into their burrows; +but, as in the case of the pine-leaves, they worked in a rather +careless manner, for only 44 per cent. were drawn in by the apex, +22 per cent. by the middle, and 33 per cent. by the base. In five +cases, two triangles were drawn into the same burrow. + +It may be suggested with much apparent probability that so large a +proportion of the triangles were drawn in by the apex, not from the +worms having selected this end as the most convenient for the +purpose, but from having first tried in other ways and failed. +This notion was countenanced by the manner in which worms in +confinement were seen to drag about and drop the triangles; but +then they were working carelessly. I did not at first perceive the +importance of this subject, but merely noticed that the bases of +those triangles which had been drawn in by the apex, were generally +clean and not crumpled. The subject was afterwards attended to +carefully. In the first place several triangles which had been +drawn in by the basal angles, or by the base, or a little above the +base, and which were thus much crumpled and dirtied, were left for +some hours in water and were then well shaken while immersed; but +neither the dirt nor the creases were thus removed. Only slight +creases could be obliterated, even by pulling the wet triangles +several times through my fingers. Owing to the slime from the +worms' bodies, the dirt was not easily washed off. We may +therefore conclude that if a triangle, before being dragged in by +the apex, had been dragged into a burrow by its base with even a +slight degree of force, the basal part would long retain its +creases and remain dirty. The condition of 89 triangles (65 narrow +and 24 broad ones), which had been drawn in by the apex, was +observed; and the bases of only 7 of them were at all creased, +being at the same time generally dirty. Of the 82 uncreased +triangles, 14 were dirty at the base; but it does not follow from +this fact that these had first been dragged towards the burrows by +their bases; for the worms sometimes covered large portions of the +triangles with slime, and these when dragged by the apex over the +ground would be dirtied; and during rainy weather, the triangles +were often dirtied over one whole side or over both sides. If the +worms had dragged the triangles to the mouths of their burrows by +their bases, as often as by their apices, and had then perceived, +without actually trying to draw them into the burrow, that the +broader end was not well adapted for this purpose--even in this +case a large proportion would probably have had their basal ends +dirtied. We may therefore infer--improbable as is the inference-- +that worms are able by some means to judge which is the best end by +which to draw triangles of paper into their burrows. + +The percentage results of the foregoing observations on the manner +in which worms draw various kinds of objects into the mouths of +their burrows may be abridged as follows:- + + + Drawn + into the Drawn in, Drawn in, +Nature of Object. burrows, by or by or + by or near near + near the the the + apex. middle. base. +Leaves of various kinds 80 11 9 +- of the Lime, basal margin + of blade broad, apex + acuminated 79 17 4 +- of a Laburnum, basal part of + blade as narrow as, or some- + times little narrower than + the apical part 63 10 27 +- of the Rhododendron, basal + part of blade often narrower + than the apical part 34 ... 66 +- of Pine-trees, consisting of + two needles arising from a + common base ... ... 100 +Petioles of a Clematis, + somewhat pointed at the apex, + and blunt at the base 76 ... 24 +- of the Ash, the thick basal + end often drawn in to serve + as food 48.5 ... 51.5 +- of Robinia, extremely thin, + especially towards the apex, + so as to be ill-fitted for + plugging up the burrows 44 ... 56 +Triangles of paper, of the + two sizes 62 15 23 +- of the broad ones alone 59 25 16 +- of the narrow ones alone 65 14 21 + + +If we consider these several cases, we can hardly escape from the +conclusion that worms show some degree of intelligence in their +manner of plugging up their burrows. Each particular object is +seized in too uniform a manner, and from causes which we can +generally understand, for the result to be attributed to mere +chance. That every object has not been drawn in by its pointed +end, may be accounted for by labour having been saved through some +being inserted by their broader or thicker ends. No doubt worms +are led by instinct to plug up their burrows; and it might have +been expected that they would have been led by instinct how best to +act in each particular case, independently of intelligence. We see +how difficult it is to judge whether intelligence comes into play, +for even plants might sometimes be thought to be thus directed; for +instance when displaced leaves re-direct their upper surfaces +towards the light by extremely complicated movements and by the +shortest course. With animals, actions appearing due to +intelligence may be performed through inherited habit without any +intelligence, although aboriginally thus acquired. Or the habit +may have been acquired through the preservation and inheritance of +beneficial variations of some other habit; and in this case the new +habit will have been acquired independently of intelligence +throughout the whole course of its development. There is no a +priori improbability in worms having acquired special instincts +through either of these two latter means. Nevertheless it is +incredible that instincts should have been developed in reference +to objects, such as the leaves of petioles of foreign plants, +wholly unknown to the progenitors of the worms which act in the +described manner. Nor are their actions so unvarying or inevitable +as are most true instincts. + +As worms are not guided by special instincts in each particular +case, though possessing a general instinct to plug up their +burrows, and as chance is excluded, the next most probable +conclusion seems to be that they try in many different ways to draw +in objects, and at last succeed in some one way. But it is +surprising that an animal so low in the scale as a worm should have +the capacity for acting in this manner, as many higher animals have +no such capacity. For instance, ants may be seen vainly trying to +drag an object transversely to their course, which could be easily +drawn longitudinally; though after a time they generally act in a +wiser manner, M. Fabre states {33} that a Sphex--an insect +belonging to the same highly-endowed order with ants--stocks its +nest with paralysed grass-hoppers, which are invariably dragged +into the burrow by their antennae. When these were cut off close +to the head, the Sphex seized the palpi; but when these were +likewise cut off, the attempt to drag its prey into the burrow was +given up in despair. The Sphex had not intelligence enough to +seize one of the six legs or the ovipositor of the grasshopper, +which, as M. Fabre remarks, would have served equally well. So +again, if the paralysed prey with an egg attached to it be taken +out of the cell, the Sphex after entering and finding the cell +empty, nevertheless closes it up in the usual elaborate manner. +Bees will try to escape and go on buzzing for hours on a window, +one half of which has been left open. Even a pike continued during +three months to dash and bruise itself against the glass sides of +an aquarium, in the vain attempt to seize minnows on the opposite +side. {34} A cobra-snake was seen by Mr. Layard {35} to act much +more wisely than either the pike or the Sphex; it had swallowed a +toad lying within a hole, and could not withdraw its head; the toad +was disgorged, and began to crawl away; it was again swallowed and +again disgorged; and now the snake had learnt by experience, for it +seized the toad by one of its legs and drew it out of the hole. +The instincts of even the higher animals are often followed in a +senseless or purposeless manner: the weaver-bird will +perseveringly wind threads through the bars of its cage, as if +building a nest: a squirrel will pat nuts on a wooden floor, as if +he had just buried them in the ground: a beaver will cut up logs +of wood and drag them about, though there is no water to dam up; +and so in many other cases. + +Mr. Romanes, who has specially studied the minds of animals, +believes that we can safely infer intelligence, only when we see an +individual profiting by its own experience. By this test the cobra +showed some intelligence; but this would have been much plainer if +on a second occasion he had drawn a toad out of a hole by its leg. +The Sphex failed signally in this respect. Now if worms try to +drag objects into their burrows first in one way and then in +another, until they at last succeed, they profit, at least in each +particular instance, by experience. + +But evidence has been advanced showing that worms do not habitually +try to draw objects into their burrows in many different ways. +Thus half-decayed lime-leaves from their flexibility could have +been drawn in by their middle or basal parts, and were thus drawn +into the burrows in considerable numbers; yet a large majority were +drawn in by or near the apex. The petioles of the Clematis could +certainly have been drawn in with equal ease by the base and apex; +yet three times and in certain cases five times as many were drawn +in by the apex as by the base. It might have been thought that the +foot-stalks of leaves would have tempted the worms as a convenient +handle; yet they are not largely used, except when the base of the +blade is narrower than the apex. A large number of the petioles of +the ash are drawn in by the base; but this part serves the worms as +food. In the case of pine-leaves worms plainly show that they at +least do not seize the leaf by chance; but their choice does not +appear to be determined by the divergence of the two needles, and +the consequent advantage or necessity of drawing them into their +burrows by the base. With respect to the triangles of paper, those +which had been drawn in by the apex rarely had their bases creased +or dirty; and this shows that the worms had not often first tried +to drag them in by this end. + +If worms are able to judge, either before drawing or after having +drawn an object close to the mouths of their burrows, how best to +drag it in, they must acquire some notion of its general shape. +This they probably acquire by touching it in many places with the +anterior extremity of their bodies, which serves as a tactile +organ. It may be well to remember how perfect the sense of touch +becomes in a man when born blind and deaf, as are worms. If worms +have the power of acquiring some notion, however rude, of the shape +of an object and of their burrows, as seems to be the case, they +deserve to be called intelligent; for they then act in nearly the +same manner as would a man under similar circumstances. + +To sum up, as chance does not determine the manner in which objects +are drawn into the burrows, and as the existence of specialized +instincts for each particular case cannot be admitted, the first +and most natural supposition is that worms try all methods until +they at last succeed; but many appearances are opposed to such a +supposition. One alternative alone is left, namely, that worms, +although standing low in the scale of organization, possess some +degree of intelligence. This will strike every one as very +improbable; but it may be doubted whether we know enough about the +nervous system of the lower animals to justify our natural distrust +of such a conclusion. With respect to the small size of the +cerebral ganglia, we should remember what a mass of inherited +knowledge, with some power of adapting means to an end, is crowded +into the minute brain of a worker-ant. + +Means by which worms excavate their burrows.--This is effected in +two ways; by pushing away the earth on all sides, and by swallowing +it. In the former case, the worm inserts the stretched out and +attenuated anterior extremity of its body into any little crevice, +or hole; and then, as Perrier remarks, {36} the pharynx is pushed +forwards into this part, which consequently swells and pushes away +the earth on all sides. The anterior extremity thus serves as a +wedge. It also serves, as we have before seen, for prehension and +suction, and as a tactile organ. A worm was placed on loose mould, +and it buried itself in between two and three minutes. On another +occasion four worms disappeared in 15 minutes between the sides of +the pot and the earth, which had been moderately pressed down. On +a third occasion three large worms and a small one were placed on +loose mould well mixed with fine sand and firmly pressed down, and +they all disappeared, except the tail of one, in 35 minutes. On a +fourth occasion six large worms were placed on argillaceous mud +mixed with sand firmly pressed down, and they disappeared, except +the extreme tips of the tails of two of them, in 40 minutes. In +none of these cases, did the worms swallow, as far as could be +seen, any earth. They generally entered the ground close to the +sides of the pot. + +A pot was next filled with very fine ferruginous sand, which was +pressed down, well watered, and thus rendered extremely compact. A +large worm left on the surface did not succeed in penetrating it +for some hours, and did not bury itself completely until 25 hrs. 40 +min. had elapsed. This was effected by the sand being swallowed, +as was evident by the large quantity ejected from the vent, long +before the whole body had disappeared. Castings of a similar +nature continued to be ejected from the burrow during the whole of +the following day. + +As doubts have been expressed by some writers whether worms ever +swallow earth solely for the sake of making their burrows, some +additional cases may be given. A mass of fine reddish sand, 23 +inches in thickness, left on the ground for nearly two years, had +been penetrated in many places by worms; and their castings +consisted partly of the reddish sand and partly of black earth +brought up from beneath the mass. This sand had been dug up from a +considerable depth, and was of so poor a nature that weeds could +not grow on it. It is therefore highly improbable that it should +have been swallowed by the worms as food. Again in a field near my +house the castings frequently consist of almost pure chalk, which +lies at only a little depth beneath the surface; and here again it +is very improbable that the chalk should have been swallowed for +the sake of the very little organic matter which could have +percolated into it from the poor overlying pasture. Lastly, a +casting thrown up through the concrete and decayed mortar between +the tiles, with which the now ruined aisle of Beaulieu Abbey had +formerly been paved, was washed, so that the coarser matter alone +was left. This consisted of grains of quartz, micaceous slate, +other rocks, and bricks or tiles, many of them from 1/20 to 1/10 +inch in diameter. No one will suppose that these grains were +swallowed as food, yet they formed more than half of the casting, +for they weighed 19 grains, the whole casting having weighed 33 +grains. Whenever a worm burrows to a depth of some feet in +undisturbed compact ground, it must form its passage by swallowing +the earth; for it is incredible that the ground could yield on all +sides to the pressure of the pharynx when pushed forwards within +the worm's body. + +That worms swallow a larger quantity of earth for the sake of +extracting any nutritious matter which it may contain than for +making their burrows, appears to me certain. But as this old +belief has been doubted by so high an authority as Claparede, +evidence in its favour must be given in some detail. There is no a +priori improbability in such a belief, for besides other annelids, +especially the Arenicola marina, which throws up such a profusion +of castings on our tidal sands, and which it is believed thus +subsists, there are animals belonging to the most distinct classes, +which do not burrow, but habitually swallow large quantities of +sand; namely, the molluscan Onchidium and many Echinoderms. {37} + +If earth were swallowed only when worms deepened their burrows or +made new ones, castings would be thrown up only occasionally; but +in many places fresh castings may be seen every morning, and the +amount of earth ejected from the same burrow on successive days is +large. Yet worms do not burrow to a great depth, except when the +weather is very dry or intensely cold. On my lawn the black +vegetable mould or humus is only about 5 inches in thickness, and +overlies light-coloured or reddish clayey soil: now when castings +are thrown up in the greatest profusion, only a small proportion +are light coloured, and it is incredible that the worms should +daily make fresh burrows in every direction in the thin superficial +layer of dark-coloured mould, unless they obtained nutriment of +some kind from it. I have observed a strictly analogous case in a +field near my house where bright red clay lay close beneath the +surface. Again on one part of the Downs near Winchester the +vegetable mould overlying the chalk was found to be only from 3 to +4 inches in thickness; and the many castings here ejected were as +black as ink and did not effervesce with acids; so that the worms +must have confined themselves to this thin superficial layer of +mould, of which large quantities were daily swallowed. In another +place at no great distance the castings were white; and why the +worms should have burrowed into the chalk in some places and not in +others, I am unable to conjecture. + +Two great piles of leaves had been left to decay in my grounds, and +months after their removal, the bare surface, several yards in +diameter, was so thickly covered during several months with +castings that they formed an almost continuous layer; and the large +number of worms which lived here must have subsisted during these +months on nutritious matter contained in the black earth. + +The lowest layer from another pile of decayed leaves mixed with +some earth was examined under a high power, and the number of +spores of various shapes and sizes which it contained was +astonishingly great; and these crushed in the gizzards of worms may +largely aid in supporting them. Whenever castings are thrown up in +the greatest number, few or no leaves are drawn into the burrows; +for instance the turf along a hedgerow, about 200 yards in length, +was daily observed in the autumn during several weeks, and every +morning many fresh castings were seen; but not a single leaf was +drawn into these burrows. These castings from their blackness and +from the nature of the subsoil could not have been brought up from +a greater depth than 6 or 8 inches. On what could these worms have +subsisted during this whole time, if not on matter contained in the +black earth? On the other hand, whenever a large number of leaves +are drawn into the burrows, the worms seem to subsist chiefly on +them, for few earth-castings are then ejected on the surface. This +difference in the behaviour of worms at different times, perhaps +explains a statement by Claparede, namely, that triturated leaves +and earth are always found in distinct parts of their intestines. + +Worms sometimes abound in places where they can rarely or never +obtain dead or living leaves; for instance, beneath the pavement in +well-swept courtyards, into which leaves are only occasionally +blown. My son Horace examined a house, one corner of which had +subsided; and he found here in the cellar, which was extremely +damp, many small worm-castings thrown up between the stones with +which the cellar was paved; and in this case it is improbable that +the worms could ever have obtained leaves. Mr. A. C. Horner +confirms this account, as he has seen castings in the cellars of +his house, which is an old one at Tonbridge. + +But the best evidence, known to me, of worms subsisting for at +least considerable periods of time solely on the organic matter +contained in earth, is afforded by some facts communicated to me by +Dr. King. Near Nice large castings abound in extraordinary +numbers, so that 5 or 6 were often found within the space of a +square foot. They consist of fine, pale-coloured earth, containing +calcareous matter, which after having passed through the bodies of +worms and being dried, coheres with considerable force. I have +reason to believe that these castings had been formed by species of +Perichaeta, which have been naturalized here from the East. {38} +They rise like towers, with their summits often a little broader +than their bases, sometimes to a height of above 3 and often to a +height of 2.5 inches. The tallest of those which were measured was +3.3 inches in height and 1 inch in diameter. A small cylindrical +passage runs up the centre of each tower, through which the worm +ascends to eject the earth which it has swallowed, and thus to add +to its height. A structure of this kind would not allow leaves +being easily dragged from the surrounding ground into the burrows; +and Dr. King, who looked carefully, never saw even a fragment of a +leaf thus drawn in. Nor could any trace be discovered of the worms +having crawled down the exterior surfaces of the towers in search +of leaves; and had they done so, tracks would almost certainly have +been left on the upper part whilst it remained soft. It does not, +however, follow that these worms do not draw leaves into their +burrows during some other season of the year, at which time they +would not build up their towers. + +From the several foregoing cases, it can hardly be doubted that +worms swallow earth, not only for the sake of making their burrows, +but for obtaining food. Hensen, however, concludes from his +analyses of mould that worms probably could not live on ordinary +vegetable mould, though he admits that they might be nourished to +some extent by leaf-mould. {39} But we have seen that worms +eagerly devour raw meat, fat, and dead worms; and ordinary mould +can hardly fail to contain many ova, larvae, and small living or +dead creatures, spores of cryptogamic plants, and micrococci, such +as those which give rise to saltpetre. These various organisms, +together with some cellulose from any leaves and roots not utterly +decayed, might well account for such large quantities of mould +being swallowed by worms. It may be worth while here to recall the +fact that certain species of Utricularia, which grow in damp places +in the tropics, possess bladders beautifully constructed for +catching minute subterranean animals; and these traps would not +have been developed unless many small animals inhabited such soil. + +The depth to which worms penetrate, and the construction of their +burrows.--Although worms usually live near the surface, yet they +burrow to a considerable depth during long-continued dry weather +and severe cold. In Scandinavia, according to Eisen, and in +Scotland, according to Mr. Lindsay Carnagie, the burrows run down +to a depth of from 7 to 8 feet; in North Germany, according to +Hoffmeister, from 6 to 8 feet, but Hensen says, from 3 to 6 feet. +This latter observer has seen worms frozen at a depth of 1.5 feet +beneath the surface. I have not myself had many opportunities for +observation, but I have often met with worms at depths of 3 to 4 +feet. In a bed of fine sand overlying the chalk, which had never +been disturbed, a worm was cut into two at 55 inches, and another +was found here at Down in December at the bottom of its burrow, at +61 inches beneath the surface. Lastly, in earth near an old Roman +Villa, which had not been disturbed for many centuries, a worm was +met with at a depth of 66 inches; and this was in the middle of +August. + +The burrows run down perpendicularly, or more commonly a little +obliquely. They are said sometimes to branch, but as far as I have +seen this does not occur, except in recently dug ground and near +the surface. They are generally, or as I believe invariably, lined +with a thin layer of fine, dark-coloured earth voided by the worms; +so that they must at first be made a little wider than their +ultimate diameter. I have seen several burrows in undisturbed sand +thus lined at a depth of 4 ft. 6 in.; and others close to the +surface thus lined in recently dug ground. The walls of fresh +burrows are often dotted with little globular pellets of voided +earth, still soft and viscid; and these, as it appears, are spread +out on all sides by the worm as it travels up or down its burrow. +The lining thus formed becomes very compact and smooth when nearly +dry, and closely fits the worm's body. The minute reflexed +bristles which project in rows on all sides from the body, thus +have excellent points of support; and the burrow is rendered well +adapted for the rapid movement of the animal. The lining appears +also to strengthen the walls, and perhaps saves the worm's body +from being scratched. I think so because several burrows which +passed through a layer of sifted coal-cinders, spread over turf to +a thickness of 1.5 inch, had been thus lined to an unusual +thickness. In this case the worms, judging from the castings, had +pushed the cinders away on all sides and had not swallowed any of +them. In another place, burrows similarly lined, passed through a +layer of coarse coal-cinders, 3.5 inches in thickness. We thus see +that the burrows are not mere excavations, but may rather be +compared with tunnels lined with cement. + +The mouths of the burrow are in addition often lined with leaves; +and this is an instinct distinct from that of plugging them up, and +does not appear to have been hitherto noticed. Many leaves of the +Scotch-fir or pine (Pinus sylvestris) were given to worms kept in +confinement in two pots; and when after several weeks the earth was +carefully broken up, the upper parts of three oblique burrows were +found surrounded for lengths of 7, 4, and 3.5 inches with pine- +leaves, together with fragments of other leaves which had been +given the worms as food. Glass beads and bits of tile, which had +been strewed on the surface of the soil, were stuck into the +interstices between the pine-leaves; and these interstices were +likewise plastered with the viscid castings voided by the worms. +The structures thus formed cohered so well, that I succeeded in +removing one with only a little earth adhering to it. It consisted +of a slightly curved cylindrical case, the interior of which could +be seen through holes in the sides and at either end. The pine- +leaves had all been drawn in by their bases; and the sharp points +of the needles had been pressed into the lining of voided earth. +Had this not been effectually done, the sharp points would have +prevented the retreat of the worms into their burrows; and these +structures would have resembled traps armed with converging points +of wire, rendering the ingress of an animal easy and its egress +difficult or impossible. The skill shown by these worms is +noteworthy and is the more remarkable, as the Scotch pine is not a +native of this district. + +After having examined these burrows made by worms in confinement, I +looked at those in a flower-bed near some Scotch pines. These had +all been plugged up in the ordinary manner with the leaves of this +tree, drawn in for a length of from 1 to 1.5 inch; but the mouths +of many of them were likewise lined with them, mingled with +fragments of other kinds of leaves, drawn in to a depth of 4 or 5 +inches. Worms often remain, as formerly stated, for a long time +close to the mouths of their burrows, apparently for warmth; and +the basket-like structures formed of leaves would keep their bodies +from coming into close contact with the cold damp earth. That they +habitually rested on the pine-leaves, was rendered probable by +their clean and almost polished surfaces. + +The burrows which run far down into the ground, generally, or at +least often, terminate in a little enlargement or chamber. Here, +according to Hoffmeister, one or several worms pass the winter +rolled up into a ball. Mr. Lindsay Carnagie informed me (1838) +that he had examined many burrows over a stone-quarry in Scotland, +where the overlying boulder-clay and mould had recently been +cleared away, and a little vertical cliff thus left. In several +cases the same burrow was a little enlarged at two or three points +one beneath the other; and all the burrows terminated in a rather +large chamber, at a depth of 7 or 8 feet from the surface. These +chambers contained many small sharp bits of stone and husks of +flax-seeds. They must also have contained living seeds, for on the +following spring Mr. Carnagie saw grass-plants sprouting out of +some of the intersected chambers. I found at Abinger in Surrey two +burrows terminating in similar chambers at a depth of 36 and 41 +inches, and these were lined or paved with little pebbles, about as +large as mustard seeds; and in one of the chambers there was a +decayed oat-grain, with its husk. Hensen likewise states that the +bottoms of the burrows are lined with little stones; and where +these could not be procured, seeds, apparently of the pear, had +been used, as many as fifteen having been carried down into a +single burrow, one of which had germinated. {40} We thus see how +easily a botanist might be deceived who wished to learn how long +deeply buried seeds remained alive, if he were to collect earth +from a considerable depth, on the supposition that it could contain +only seeds which had long lain buried. It is probable that the +little stones, as well as the seeds, are carried down from the +surface by being swallowed; for a surprising number of glass beads, +bits of tile and of glass were certainly thus carried down by worms +kept in pots; but some may have been carried down within their +mouths. The sole conjecture which I can form why worms line their +winter-quarters with little stones and seeds, is to prevent their +closely coiled-up bodies from coming into close contact with the +surrounding cold soil; and such contact would perhaps interfere +with their respiration which is effected by the skin alone. + +A worm after swallowing earth, whether for making its burrow or for +food, soon comes to the surface to empty its body. The ejected +earth is thoroughly mingled with the intestinal secretions, and is +thus rendered viscid. After being dried it sets hard. I have +watched worms during the act of ejection, and when the earth was in +a very liquid state it was ejected in little spurts, and by a slow +peristaltic movement when not so liquid. It is not cast +indifferently on any side, but with some care, first on one and +then on another side; the tail being used almost like a trowel. +When a worm comes to the surface to eject earth, the tail +protrudes, but when it collects leaves its head must protrude. +Worms therefore must have the power of turning round in their +closely-fitting burrows; and this, as it appears to us, would be a +difficult feat. As soon as a little heap has been formed, the worm +apparently avoids, for the sake of safety, protruding its tail; and +the earthy matter is forced up through the previously deposited +soft mass. The mouth of the same burrow is used for this purpose +for a considerable time. In the case of the tower-like castings +(see Fig. 2) near Nice, and of the similar but still taller towers +from Bengal (hereafter to be described and figured), a considerable +degree of skill is exhibited in their construction. Dr. King also +observed that the passage up these towers hardly ever ran in the +same exact line with the underlying burrow, so that a thin +cylindrical object such as a haulm of grass, could not be passed +down the tower into the burrow; and this change of direction +probably serves in some manner as a protection. + +Worms do not always eject their castings on the surface of the +ground. When they can find any cavity, as when burrowing in newly +turned-up earth, or between the stems of banked-up plants, they +deposit their castings in such places. So again any hollow beneath +a large stone lying on the surface of the ground, is soon filled up +with their castings. According to Hensen, old burrows are +habitually used for this purpose; but as far as my experience +serves, this is not the case, excepting with those near the surface +in recently dug ground. I think that Hensen may have been deceived +by the walls of old burrows, lined with black earth, having sunk in +or collapsed; for black streaks are thus left, and these are +conspicuous when passing through light-coloured soil, and might be +mistaken for completely filled-up burrows. + +It is certain that old burrows collapse in the course of time; for +as we shall see in the next chapter, the fine earth voided by +worms, if spread out uniformly, would form in many places in the +course of a year a layer 0.2 of an inch in thickness; so that at +any rate this large amount is not deposited within the old unused +burrows. If the burrows did not collapse, the whole ground would +be first thickly riddled with holes to a depth of about ten inches, +and in fifty years a hollow unsupported space, ten inches in depth, +would be left. The holes left by the decay of successively formed +roots of trees and plants must likewise collapse in the course of +time. + +The burrows of worms run down perpendicularly or a little +obliquely, and where the soil is at all argillaceous, there is no +difficulty in believing that the walls would slowly flow or slide +inwards during very wet weather. When, however, the soil is sandy +or mingled with many small stones, it can hardly be viscous enough +to flow inwards during even the wettest weather; but another agency +may here come into play. After much rain the ground swells, and as +it cannot expand laterally, the surface rises; during dry weather +it sinks again. For instance, a large flat stone laid on the +surface of a field sank 3.33 mm. whilst the weather was dry between +May 9th and June 13th, and rose 1.91 mm, between September 7th and +19th of the same year, much rain having fallen during the latter +part of this time. During frosts and thaws the movements were +twice as great. These observations were made by my son Horace, who +will hereafter publish an account of the movements of this stone +during successive wet and dry seasons, and of the effects of its +being undermined by worms. Now when the ground swells, if it be +penetrated by cylindrical holes, such as worm-burrows, their walls +will tend to yield and be pressed inwards; and the yielding will be +greater in the deeper parts (supposing the whole to be equally +moistened) from the greater weight of the superincumbent soil which +has to be raised, than in the parts near the surface. When the +ground dries, the walls will shrink a little and the burrows will +be a little enlarged. Their enlargement, however, through the +lateral contraction of the ground, will not be favoured, but rather +opposed, by the weight of the superincumbent soil. + +Distribution of Worms.--Earth-worms are found in all parts of the +world, and some of the genera have an enormous range. {41} They +inhabit the most isolated islands; they abound in Iceland, and are +known to exist in the West Indies, St. Helena, Madagascar, New +Caledonia and Tahiti. In the Antarctic regions, worms from +Kerguelen Land have been described by Ray Lankester; and I found +them in the Falkland Islands. How they reach such isolated islands +is at present quite unknown. They are easily killed by salt-water, +and it does not appear probable that young worms or their egg- +capsules could be carried in earth adhering to the feet or beaks of +land-birds. Moreover Kerguelen Land is not now inhabited by any +land-bird. + +In this volume we are chiefly concerned with the earth cast up by +worms, and I have gleaned a few facts on this subject with respect +to distant lands. Worms throw up plenty of castings in the United +States. In Venezuela, castings, probably ejected by species of +Urochaeta, are common in the gardens and fields, but not in the +forests, as I hear from Dr. Ernst of Caracas. He collected 156 +castings from the court-yard of his house, having an area of 200 +square yards. They varied in bulk from half a cubic centimeter to +five cubic centimeters, and were on an average three cubic +centimeters. They were, therefore, of small size in comparison +with those often found in England; for six large castings from a +field near my house averaged 16 cubic centimeters. Several species +of earth-worms are common in St. Catharina in South Brazil, and +Fritz Muller informs me "that in most parts of the forests and +pasture-lands, the whole soil, to a depth of a quarter of a metre, +looks as if it had passed repeatedly through the intestines of +earth-worms, even where hardly any castings are to be seen on the +surface." A gigantic but very rare species is found there, the +burrows of which are sometimes even two centimeters or nearly 0.8 +of an inch in diameter, and which apparently penetrate the ground +to a great depth. + +In the dry climate of New South Wales, I hardly expected that worms +would be common; but Dr. G. Krefft of Sydney, to whom I applied, +after making inquiries from gardeners and others, and from his own +observations, informs me that their castings abound. He sent me +some collected after heavy rain, and they consisted of little +pellets, about 0.15 inch in diameter; and the blackened sandy earth +of which they were formed still cohered with considerable tenacity. + +The late Mr. John Scott of the Botanic Gardens near Calcutta made +many observations for me on worms living under the hot and humid +climate of Bengal. The castings abound almost everywhere, in +jungles and in the open ground, to a greater degree, as he thinks, +than in England. After the water has subsided from the flooded +rice-fields, the whole surface very soon becomes studded with +castings--a fact which much surprised Mr. Scott, as he did not know +how long worms could survive beneath water. They cause much +trouble in the Botanic garden, "for some of the finest of our lawns +can be kept in anything like order only by being almost daily +rolled; if left undisturbed for a few days they become studded with +large castings." These closely resemble those described as +abounding near Nice; and they are probably the work of a species of +Perichaeta. They stand up like towers, with an open passage in the +centre. + +A figure of one of these castings from a photograph is here given +(Fig. 3). The largest received by me was 3.5 inches in height and +1.35 inch in diameter; another was only 0.75 inch in diameter and +2.75 in height. In the following year, Mr. Scott measured several +of the largest; one was 6 inches in height and nearly 1.5 in +diameter: two others were 5 inches in height and respectively 2 +and rather more than 2.5 inches in diameter. The average weight of +the 22 castings sent to me was 35 grammes (1.25 oz.); and one of +them weighed 44.8 grammes (or 2 oz.). All these castings were +thrown up either in one night or in two. Where the ground in +Bengal is dry, as under large trees, castings of a different kind +are found in vast numbers: these consist of little oval or conical +bodies, from about the 1/20 to rather above 1/10 of an inch in +length. They are obviously voided by a distinct species of worms. + +The period during which worms near Calcutta display such +extraordinary activity lasts for only a little over two months, +namely, during the cool season after the rains. At this time they +are generally found within about 10 inches beneath the surface. +During the hot season they burrow to a greater depth, and are then +found coiled up and apparently hybernating. Mr. Scott has never +seen them at a greater depth than 2.5 feet, but has heard of their +having been found at 4 feet. Within the forests, fresh castings +may be found even during the hot season. The worms in the Botanic +garden, during the cool and dry season, draw many leaves and little +sticks into the mouths of their burrows, like our English worms; +but they rarely act in this manner during the rainy season. + +Mr. Scott saw worm-castings on the lofty mountains of Sikkim in +North India. In South India Dr. King found in one place, on the +plateau of the Nilgiris, at an elevation of 7000 feet, "a good many +castings," which are interesting for their great size. The worms +which eject them are seen only during the wet season, and are +reported to be from 12 to 15 inches in length, and as thick as a +man's little finger. These castings were collected by Dr. King +after a period of 110 days without any rain; and they must have +been ejected either during the north-east or more probably during +the previous south-west monsoon; for their surfaces had suffered +some disintegration and they were penetrated by many fine roots. A +drawing is here given (Fig. 4) of one which seems to have best +retained its original size and appearance. Notwithstanding some +loss from disintegration, five of the largest of these castings +(after having been well sun-dried) weighed each on an average 89.5 +grammes, or above 3 oz.; and the largest weighed 123.14 grammes, or +4.33 oz.,--that is, above a quarter of a pound! The largest +convolutions were rather more than one inch in diameter; but it is +probable that they had subsided a little whilst soft, and that +their diameters had thus been increased. Some had flowed so much +that they now consisted of a pile of almost flat confluent cakes. +All were formed of fine, rather light-coloured earth, and were +surprisingly hard and compact, owing no doubt to the animal matter +by which the particles of earth had been cemented together. They +did not disintegrate, even when left for some hours in water. +Although they had been cast up on the surface of gravelly soil, +they contained extremely few bits of rock, the largest of which was +only 0.15 inch in diameter. + +Dr. King saw in Ceylon a worm about 2 feet in length and 0.5 inch +in diameter; and he was told that it was a very common species +during the wet season. These worms must throw up castings at least +as large as those on the Nilgiri Mountains; but Dr. King saw none +during his short visit to Ceylon. + +Sufficient facts have now been given, showing that worms do much +work in bringing up fine earth to the surface in most or all parts +of the world, and under the most different climates. + + + +CHAPTER III--THE AMOUNT OF FINE EARTH BROUGHT UP BY WORMS TO THE +SURFACE. + + + +Rate at which various objects strewed on the surface of grass- +fields are covered up by the castings of worms--The burial of a +paved path--The slow subsidence of great stones left on the +surface--The number of worms which live within a given space--The +weight of earth ejected from a burrow, and from all the burrows +within a given space--The thickness of the layer of mould which the +castings on a given space would form within a given time if +uniformly spread out--The slow rate at which mould can increase to +a great thickness--Conclusion. + + +We now come to the more immediate subject of this volume, namely, +the amount of earth which is brought up by worms from beneath the +surface, and is afterwards spread out more or less completely by +the rain and wind. The amount can be judged of by two methods,--by +the rate at which objects left on the surface are buried, and more +accurately by weighing the quantity brought up within a given time. +We will begin with the first method, as it was first followed. + +Near Mael Hall in Staffordshire, quick-lime had been spread about +the year 1827 thickly over a field of good pasture-land, which had +not since been ploughed. Some square holes were dug in this field +in the beginning of October 1837; and the sections showed a layer +of turf, formed by the matted roots of the grasses, 0.5 inch in +thickness, beneath which, at a depth of 2.5 inches (or 3 inches +from the surface), a layer of the lime in powder or in small lumps +could be distinctly seen running all round the vertical sides of +the holes. The soil beneath the layer of lime was either gravelly +or of a coarse sandy nature, and differed considerably in +appearance from the overlying dark-coloured fine mould. Coal- +cinders had been spread over a part of this same field either in +the year 1833 or 1834; and when the above holes were dug, that is +after an interval of 3 or 4 years, the cinders formed a line of +black spots round the holes, at a depth of 1 inch beneath the +surface, parallel to and above the white layer of lime. Over +another part of this field cinders had been strewed, only about +half-a-year before, and these either still lay on the surface or +were entangled among the roots of the grasses; and I here saw the +commencement of the burying process, for worm-castings had been +heaped on several of the smaller fragments. After an interval of +4.75 years this field was re-examined, and now the two layers of +lime and cinders were found almost everywhere at a greater depth +than before by nearly 1 inch, we will say by 0.75 of an inch. +Therefore mould to an average thickness of 0.22 of an inch had been +annually brought up by the worms, and had been spread over the +surface of this field. + +Coal-cinders had been strewed over another field, at a date which +could not be positively ascertained, so thickly that they formed +(October, 1837) a layer, 1 inch in thickness at a depth of about 3 +inches from the surface. The layer was so continuous that the +over-lying dark vegetable mould was connected with the sub-soil of +red clay only by the roots of the grasses; and when these were +broken, the mould and the red clay fell apart. In a third field, +on which coal-cinders and burnt marl had been strewed several times +at unknown dates, holes were dug in 1842; and a layer of cinders +could be traced at a depth of 3.5 inches, beneath which at a depth +of 9.5 inches from the surface there was a line of cinders together +with burnt marl. On the sides of one hole there were two layers of +cinders, at 2 and 3.5 inches beneath the surface; and below them at +a depth in parts of 9.5, and in other parts of 10.5 inches there +were fragments of burnt marl. In a fourth field two layers of +lime, one above the other, could be distinctly traced, and beneath +them a layer of cinders and burnt marl at a depth of from 10 to 12 +inches below the surface. + +A piece of waste, swampy land was enclosed, drained, ploughed, +harrowed and thickly covered in the year 1822 with burnt marl and +cinders. It was sowed with grass seeds, and now supports a +tolerably good but coarse pasture. Holes were dug in this field in +1837, or 15 years after its reclamation, and we see in the +accompanying diagram (Fig. 5), reduced to half of the natural +scale, that the turf was 1 inch thick, beneath which there was a +layer of vegetable mould 2.5 inches thick. This layer did not +contain fragments of any kind; but beneath it there was a layer of +mould, 1.5 inch in thickness, full of fragments of burnt marl, +conspicuous from their red colour, one of which near the bottom was +an inch in length; and other fragments of coal-cinders together +with a few white quartz pebbles. Beneath this layer and at a depth +of 4.5 inches from the surface, the original black, peaty, sandy +soil with a few quartz pebbles was encountered. Here therefore the +fragments of burnt marl and cinders had been covered in the course +of 15 years by a layer of fine vegetable mould, only 2.5 inches in +thickness, excluding the turf. Six and a half years subsequently +this field was re-examined, and the fragments were now found at +from 4 to 5 inches beneath the surface. So that in this interval +of 6.5 years, about 1.5 inch of mould had been added to the +superficial layer. I am surprised that a greater quantity had not +been brought up during the whole 21.5 years, for in the closely +underlying black, peaty soil there were many worms. It is, +however, probable that formerly, whilst the land remained poor, +worms were scanty; and the mould would then have accumulated +slowly. The average annual increase of thickness for the whole +period is 0.19 of an inch. + +Two other cases are worth recording. In the spring of 1835, a +field, which had long existed as poor pasture and was so swampy +that it trembled slightly when stamped on, was thickly covered with +red sand so that the whole surface appeared at first bright red. +When holes were dug in this field after an interval of about 2.5 +years, the sand formed a layer at a depth of 0.75 in. beneath the +surface. In 1842 (i.e., 7 years after the sand had been laid on) +fresh holes were dug, and now the red sand formed a distinct layer, +2 inches beneath the surface, or 1.5 inch beneath the turf; so that +on an average, 0.21 inch of mould had been annually brought to the +surface. Immediately beneath the layer of red sand, the original +substratum of black sandy peat extended. + +A grass field, likewise not far from Maer Hall, had formerly been +thickly covered with marl, and was then left for several years as +pasture; it was afterwards ploughed. A friend had three trenches +dug in this field 28 years after the application of the marl, {42} +and a layer of the marl fragments could be traced at a depth, +carefully measured, of 12 inches in some parts, and of 14 inches in +other parts. This difference in depth depended on the layer being +horizontal, whilst the surface consisted of ridges and furrows from +the field having been ploughed. The tenant assured me that it had +never been turned up to a greater depth than from 6 to 8 inches; +and as the fragments formed an unbroken horizontal layer from 12 to +14 inches beneath the surface, these must have been buried by the +worms whilst the land was in pasture before it was ploughed, for +otherwise they would have been indiscriminately scattered by the +plough throughout the whole thickness of the soil. Four-and-a-half +years afterwards I had three holes dug in this field, in which +potatoes had been lately planted, and the layer of marl-fragments +was now found 13 inches beneath the bottoms of the furrows, and +therefore probably 15 inches beneath the general level of the +field. It should, however, be observed that the thickness of the +blackish sandy soil, which had been thrown up by the worms above +the marl-fragments in the course of 32.5 years, would have measured +less than 15 inches, if the field had always remained as pasture, +for the soil would in this case have been much more compact. The +fragments of marl almost rested on an undisturbed substratum of +white sand with quartz pebbles; and as this would be little +attractive to worms, the mould would hereafter be very slowly +increased by their action. + +We will now give some cases of the action of worms, on land +differing widely from the dry sandy or the swampy pastures just +described. The chalk formation extends all round my house in Kent; +and its surface, from having been exposed during an immense period +to the dissolving action of rain-water, is extremely irregular, +being abruptly festooned and penetrated by many deep well-like +cavities. {43} During the dissolution of the chalk, the insoluble +matter, including a vast number of unrolled flints of all sizes, +has been left on the surface and forms a bed of stiff red clay, +full of flints, and generally from 6 to 14 feet in thickness. Over +the red clay, wherever the land has long remained as pasture, there +is a layer a few inches in thickness, of dark-coloured vegetable +mould. + +A quantity of broken chalk was spread, on December 20, 1842, over a +part of a field near my house, which had existed as pasture +certainly for 30, probably for twice or thrice as many years. The +chalk was laid on the land for the sake of observing at some future +period to what depth it would become buried. At the end of +November, 1871, that is after an interval of 29 years, a trench was +dug across this part of the field; and a line of white nodules +could be traced on both sides of the trench, at a depth of 7 inches +from the surface. The mould, therefore, (excluding the turf) had +here been thrown up at an average rate of 0.22 inch per year. +Beneath the line of chalk nodules there was in parts hardly any +fine earth free of flints, while in other parts there was a layer, +2.25 inches in thickness. In this latter case the mould was +altogether 9.25 inches thick; and in one such spot a nodule of +chalk and a smooth flint pebble, both of which must have been left +at some former time on the surface, were found at this depth. At +from 11 to 12 inches beneath the surface, the undisturbed reddish +clay, full of flints, extended. The appearance of the above +nodules of chalk surprised me, much at first, as they closely +resembled water-worn pebbles, whereas the freshly-broken fragments +had been angular. But on examining the nodules with a lens, they +no longer appeared water-worn, for their surfaces were pitted +through unequal corrosion, and minute, sharp points, formed of +broken fossil shells, projected from them. It was evident that the +corners of the original fragments of chalk had been wholly +dissolved, from presenting a large surface to the carbonic acid +dissolved in the rain-water and to that generated in soil +containing vegetable matter, as well as to the humus-acids. {44} +The projecting corners would also, relatively to the other parts, +have been embraced by a larger number of living rootlets; and these +have the power of even attacking marble, as Sachs has shown. Thus, +in the course of 29 years, buried angular fragments of chalk had +been converted into well-rounded nodules. + +Another part of this same field was mossy, and as it was thought +that sifted coal-cinders would improve the pasture, a thick layer +was spread over this part either in 1842 or 1843, and another layer +some years afterwards. In 1871 a trench was here dug, and many +cinders lay in a line at a depth of 7 inches beneath the surface, +with another line at a depth of 5.5 inches parallel to the one +beneath. In another part of this field, which had formerly existed +as a separate one, and which it was believed had been pasture-land +for more than a century, trenches were dug to see how thick the +vegetable mould was. By chance the first trench was made at a spot +where at some former period, certainly more than forty years +before, a large hole had been filled up with coarse red clay, +flints, fragments of chalk, and gravel; and here the fine vegetable +mould was only from 4.125 to 4.375 inches in thickness. In another +and undisturbed place, the mould varied much in thickness, namely, +from 6.5 to 8.5 inches; beneath which a few small fragments of +brick were found in one place. From these several cases, it would +appear that during the last 29 years mould has been heaped on the +surface at an average annual rate of from 0.2 to 0.22 of an inch. +But in this district when a ploughed field is first laid down in +grass, the mould accumulates at a much slower rate. The rate, +also, must become very much slower after a bed of mould, several +inches in thickness, has been formed; for the worms then live +chiefly near the surface, and burrow down to a greater depth so as +to bring up fresh earth from below, only during the winter when the +weather is very cold (at which time worms were found in this field +at a depth of 26 inches) and during summer, when the weather is +very dry. + +A field, which adjoins the one just described, slopes in one part +rather steeply (viz., at from 10 degrees to 15 degrees); this part +was last ploughed in 1841, was then harrowed and left to become +pasture-land. For several years it was clothed with an extremely +scant vegetation, and was so thickly covered with small and large +flints (some of them half as large as a child's head) that the +field was always called by my sons "the stony field." When they +ran down the slope the stones clattered together, I remember +doubting whether I should live to see these larger flints covered +with vegetable mould and turf. But the smaller stones disappeared +before many years had elapsed, as did every one of the larger ones +after a time; so that after thirty years (1871) a horse could +gallop over the compact turf from one end of the field to the +other, and not strike a single stone with his shoes. To anyone who +remembered the appearance of the field in 1842, the transformation +was wonderful. This was certainly the work of the worms, for +though castings were not frequent for several years, yet some were +thrown up month after month, and these gradually increased in +numbers as the pasture improved. In the year 1871 a trench was dug +on the above slope, and the blades of grass were cut off close to +the roots, so that the thickness of the turf and of the vegetable +mould could be measured accurately. The turf was rather less than +half an inch, and the mould, which did not contain any stones, 2.5 +inches in thickness. Beneath this lay coarse clayey earth full of +flints, like that in any of the neighbouring ploughed fields. This +coarse earth easily fell apart from the overlying mould when a spit +was lifted up. The average rate of accumulation of the mould +during the whole thirty years was only .083 inch per year (i.e., +nearly one inch in twelve years); but the rate must have been much +slower at first, and afterwards considerably quicker. + +The transformation in the appearance of this field, which had been +effected beneath my eyes, was afterwards rendered the more +striking, when I examined in Knole Park a dense forest of lofty +beech-trees, beneath which nothing grew. Here the ground was +thickly strewed with large naked stones, and worm-castings were +almost wholly absent. Obscure lines and irregularities on the +surface indicated that the land had been cultivated some centuries +ago. It is probable that a thick wood of young beech-trees sprung +up so quickly, that time enough was not allowed for worms to cover +up the stones with their castings, before the site became unfitted +for their existence. Anyhow the contrast between the state of the +now miscalled "stony field," well stocked with worms, and the +present state of the ground beneath the old beech-trees in Knole +Park, where worms appeared to be absent, was striking. + +A narrow path running across part of my lawn was paved in 1843 with +small flagstones, set edgeways; but worms threw up many castings +and weeds grew thickly between them. During several years the path +was weeded and swept; but ultimately the weeds and worms prevailed, +and the gardener ceased to sweep, merely mowing off the weeds, as +often as the lawn was mowed. The path soon became almost covered +up, and after several years no trace of it was left. On removing, +in 1877, the thin overlying layer of turf, the small flag-stones, +all in their proper places, were found covered by an inch of fine +mould. + +Two recently published accounts of substances strewed on the +surface of pasture-land, having become buried through the action of +worms, may be here noticed. The Rev. H. C. Key had a ditch cut in +a field, over which coal-ashes had been spread, as it was believed, +eighteen years before; and on the clean-cut perpendicular sides of +the ditch, at a depth of at least seven inches, there could be +seen, for a length of 60 yards, "a distinct, very even, narrow line +of coal-ashes, mixed with small coal, perfectly parallel with the +top-sward." {45} This parallelism and the length of the section +give interest to the case. Secondly, Mr. Dancer states {46} that +crushed bones had been thickly strewed over a field; and "some +years afterwards" these were found "several inches below the +surface, at a uniform depth." + +The Rev. Mr. Zincke informs me that he has lately had an orchard +dug to the unusual depth of 4 feet. The upper 18 inches consisted +of dark-coloured vegetable mould, and the next 18 inches of sandy +loam, containing in the lower part many rolled pieces of sandstone, +with some bits of brick and tile, probably of Roman origin, as +remains of this period have been found close by. The sandy loam +rested on an indurated ferruginous pan of yellow clay, on the +surface of which two perfect celts were found. If, as seems +probable, the celts were originally left on the surface of the +land, they have since been covered up with earth 3 feet in +thickness, all of which has probably passed through the bodies of +worms, excepting the stones which may have been scattered on the +surface at different times, together with manure or by other means. +It is difficult otherwise to understand the source of the 18 inches +of sandy loam, which differed from the overlying dark vegetable +mould, after both had been burnt, only in being of a brighter red +colour, and in not being quite so fine-grained. But on this view +we must suppose that the carbon in vegetable mould, when it lies at +some little depth beneath the surface and does not continually +receive decaying vegetable matter from above, loses its dark colour +in the course of centuries; but whether this is probable I do not +know. + +Worms appear to act in the same manner in New Zealand as in Europe; +for Professor J. von Haast has described {47} a section near the +coast, consisting of mica-schist, "covered by 5 or 6 feet of loess, +above which about 12 inches of vegetable soil had accumulated." +Between the loess and the mould there was a layer from 3 to 6 +inches in thickness, consisting of "cores, implements, flakes, and +chips, all manufactured from hard basaltic rock." It is therefore +probable that the aborigines, at some former period, had left these +objects on the surface, and that they had afterwards been slowly +covered up by the castings of worms. + +Farmers in England are well aware that objects of all kinds, left +on the surface of pasture-land, after a time disappear, or, as they +say, work themselves downwards. How powdered lime, cinders, and +heavy stones, can work down, and at the same rate, through the +matted roots of a grass-covered surface, is a question which has +probably never occurred to them. {48} + +The Sinking of great Stones through the Action of Worms.--When a +stone of large size and of irregular shape is left on the surface +of the ground, it rests, of course, on the more protuberant parts; +but worms soon fill up with their castings all the hollow spaces on +the lower side; for, as Hensen remarks, they like the shelter of +stones. As soon as the hollows are filled up, the worms eject the +earth which they have swallowed beyond the circumference of the +stones; and thus the surface of the ground is raised all round the +stone. As the burrows excavated directly beneath the stone after a +time collapse, the stone sinks a little. {49} Hence it is, that +boulders which at some ancient period have rolled down from a rocky +mountain or cliff on to a meadow at its base, are always somewhat +imbedded in the soil; and, when removed, leave an exact impression +of their lower surfaces in the underlying fine mould. If, however, +a boulder is of such huge dimensions, that the earth beneath is +kept dry, such earth will not be inhabited by worms, and the +boulder will not sink into the ground. + +A lime-kiln formerly stood in a grass-field near Leith Hill Place +in Surrey, and was pulled down 35 years before my visit; all the +loose rubbish had been carted away, excepting three large stones of +quartzose sandstone, which it was thought might hereafter be of +some use. An old workman remembered that they had been left on a +bare surface of broken bricks and mortar, close to the foundations +of the kiln; but the whole surrounding surface is now covered with +turf and mould. The two largest of these stones had never since +been moved; nor could this easily have been done, as, when I had +them removed, it was the work of two men with levers. One of these +stones, and not the largest, was 64 inches long, 17 inches broad, +and from 9 to 10 inches in thickness. Its lower surface was +somewhat protuberant in the middle; and this part still rested on +broken bricks and mortar, showing the truth of the old workman's +account. Beneath the brick rubbish the natural sandy soil, full of +fragments of sandstone was found; and this could have yielded very +little, if at all, to the weight of the stone, as might have been +expected if the sub-soil had been clay. The surface of the field, +for a distance of about 9 inches round the stone, gradually sloped +up to it, and close to the stone stood in most places about 4 +inches above the surrounding ground. The base of the stone was +buried from 1 to 2 inches beneath the general level, and the upper +surface projected about 8 inches above this level, or about 4 +inches above the sloping border of turf. After the removal of the +stone it became evident that one of its pointed ends must at first +have stood clear above the ground by some inches, but its upper +surface was now on a level with the surrounding turf. When the +stone was removed, an exact cast of its lower side, forming a +shallow crateriform hollow, was left, the inner surface of which +consisted of fine black mould, excepting where the more protuberant +parts rested on the brick-rubbish. A transverse section of this +stone, together with its bed, drawn from measurements made after it +had been displaced, is here given on a scale of 0.5 inch to a foot +(Fig. 6). The turf-covered border which sloped up to the stone, +consisted of fine vegetable mould, in one part 7 inches in +thickness. This evidently consisted of worm-castings, several of +which had been recently ejected. The whole stone had sunk in the +thirty-five years, as far as I could judge, about 1.5 inch; and +this must have been due to the brick-rubbish beneath the more +protuberant parts having been undermined by worms. At this rate +the upper surface of the stone, if it had been left undisturbed, +would have sunk to the general level of the field in 247 years; but +before this could have occurred, some earth would have been washed +down by heavy rain from the castings on the raised border of turf +over the upper surface of the stone. + +The second stone was larger that the one just described, viz., 67 +inches in length, 39 in breadth, and 15 in thickness. The lower +surface was nearly flat, so that the worms must soon have been +compelled to eject their castings beyond its circumference. The +stone as a whole had sunk about 2 inches into the ground. At this +rate it would have required 262 years for its upper surface to have +sunk to the general level of the field. The upwardly sloping, +turf-covered border round the stone was broader than in the last +case, viz., from 14 to 16 inches; and why this should be so, I +could see no reason. In most parts this border was not so high as +in the last case, viz., from 2 to 2.5 inches, but in one place it +was as much as 5.5. Its average height close to the stone was +probably about 3 inches, and it thinned out to nothing. If so, a +layer of fine earth, 15 inches in breadth and 1.5 inch in average +thickness, of sufficient length to surround the whole of the much +elongated slab, must have been brought up by the worms in chief +part from beneath the stone in the course of 35 years. This amount +would be amply sufficient to account for its having sunk about 2 +inches into the ground; more especially if we bear in mind that a +good deal of the finest earth would have been washed by heavy rain +from the castings ejected on the sloping border down to the level +of the field. Some fresh castings were seen close to the stone. +Nevertheless, on digging a large hole to a depth of 18 inches where +the stone had lain, only two worms and a few burrows were seen, +although the soil was damp and seemed favourable for worms. There +were some large colonies of ants beneath the stone, and possibly +since their establishment the worms had decreased in number. + +The third stone was only about half as large as the others; and two +strong boys could together have rolled it over. I have no doubt +that it had been rolled over at a moderately recent time, for it +now lay at some distance from the two other stones at the bottom of +a little adjoining slope. It rested also on fine earth, instead of +partly on brick-rubbish. In agreement with this conclusion, the +raised surrounding border of turf was only 1 inch high in some +parts, and 2 inches in other parts. There were no colonies of ants +beneath this stone, and on digging a hole where it had lain, +several burrows and worms were found. + +At Stonehenge, some of the outer Druidical stones are now +prostrate, having fallen at a remote but unknown period; and these +have become buried to a moderate depth in the ground. They are +surrounded by sloping borders of turf, on which recent castings +were seen. Close to one of these fallen stones, which was 17 ft +long, 6 ft. broad, and 28.5 inches thick, a hole was dug; and here +the vegetable mould was at least 9.5 inches in thickness. At this +depth a flint was found, and a little higher up on one side of the +hole a fragment of glass. The base of the stone lay about 9.5 +inches beneath the level of the surrounding ground, and its upper +surface 19 inches above the ground. + +A hole was also dug close to a second huge stone, which in falling +had broken into two pieces; and this must have happened long ago, +judging from the weathered aspect of the fractured ends. The base +was buried to a depth of 10 inches, as was ascertained by driving +an iron skewer horizontally into the ground beneath it. The +vegetable mould forming the turf-covered sloping border round the +stone, on which many castings had recently been ejected, was 10 +inches in thickness; and most of this mould must have been brought +up by worms from beneath its base. At a distance of 8 yards from +the stone, the mould was only 5.5 inches in thickness (with a piece +of tobacco pipe at a depth of 4 inches), and this rested on broken +flint and chalk which could not have easily yielded to the pressure +or weight of the stone. + +A straight rod was fixed horizontally (by the aid of a spirit- +level) across a third fallen stone, which was 7 feet 9 inches long; +and the contour of the projecting parts and of the adjoining +ground, which was not quite level, was thus ascertained, as shown +in the accompanying diagram (Fig. 7) on a scale of 0.5 inch to a +foot. The turf-covered border sloped up to the stone on one side +to a height of 4 inches, and on the opposite side to only 2.5 +inches above the general level. A hole was dug on the eastern +side, and the base of the stone was here found to lie at a depth of +4 inches beneath the general level of the ground, and of 8 inches +beneath the top of the sloping turf-covered border. + + +Sufficient evidence has now been given showing that small objects +left on the surface of the land where worms abound soon get buried, +and that large stones sink slowly downwards through the same means. +Every step of the process could be followed, from the accidental +deposition of a single casting on a small object lying loose on the +surface, to its being entangled amidst the matted roots of the +turf, and lastly to its being embedded in the mould at various +depths beneath the surface. When the same field was re-examined +after the interval of a few years, such objects were found at a +greater depth than before. The straightness and regularity of the +lines formed by the imbedded objects, and their parallelism with +the surface of the land, are the most striking features of the +case; for this parallelism shows how equably the worms must have +worked; the result being, however, partly the effect of the washing +down of the fresh castings by rain. The specific gravity of the +objects does not affect their rate of sinking, as could be seen by +porous cinders, burnt marl, chalk and quartz pebbles, having all +sunk to the same depth within the same time. Considering the +nature of the substratum, which at Leith Hill Place was sandy soil +including many bits of rock, and at Stonehenge, chalk-rubble with +broken flints; considering, also, the presence of the turf-covered +sloping border of mould round the great fragments of stone at both +these places, their sinking does not appear to have been sensibly +aided by their weight, though this was considerable. {50} + +On the number of worms which live within a given space.--We will +now show, firstly, what a vast number of worms live unseen by us +beneath our feet, and, secondly, the actual weight of the earth +which they bring up to the surface within a given space and within +a given time. Hensen, who has published so full and interesting an +account of the habits of worms, {51} calculates, from the number +which he found in a measured space, that there must exist 133,000 +living worms in a hectare of land, or 53,767 in an acre. This +latter number of worms would weigh 356 pounds, taking Hensen's +standard of the weight of a single worm, namely, three grams. It +should, however, be noted that this calculation is founded on the +numbers found in a garden, and Hensen believes that worms are here +twice as numerous as in corn-fields. The above result, astonishing +though it be, seems to me credible, judging from the number of +worms which I have sometimes seen, and from the number daily +destroyed by birds without the species being exterminated. Some +barrels of bad ale were left on Mr. Miller's land, {52} in the hope +of making vinegar, but the vinegar proved bad, and the barrels were +upset. It should be premised that acetic acid is so deadly a +poison to worms that Perrier found that a glass rod dipped into +this acid and then into a considerable body of water in which worms +were immersed, invariably killed them quickly. On the morning +after the barrels had been upset, "the heaps of worms which lay +dead on the ground were so amazing, that if Mr. Miller had not seen +them, he could not have thought it possible for such numbers to +have existed in the space." As further evidence of the large +number of worms which live in the ground, Hensen states that he +found in a garden sixty-four open burrows in a space of 14.5 square +feet, that is, nine in 2 square feet. But the burrows are +sometimes much more numerous, for when digging in a grass-field +near Maer Hall, I found a cake of dry earth, as large as my two +open hands, which was penetrated by seven burrows, as large as +goose-quills. + +Weight of the earth ejected from a single burrow, and from all the +burrows within a given space.--With respect to the weight of the +earth daily ejected by worms, Hensen found that it amounted, in the +case of some worms which he kept in confinement, and which he +appears to have fed with leaves, to only 0.5 gram, or less than 8 +grains per diem. But a very much larger amount must be ejected by +worms in their natural state, at the periods when they consume +earth as food instead of leaves, and when they are making deep +burrows. This is rendered almost certain by the following weights +of the castings thrown up at the mouths of single burrows; the +whole of which appeared to have been ejected within no long time, +as was certainly the case in several instances. The castings were +dried (excepting in one specified instance) by exposure during many +days to the sun or before a hot fire. + + +WEIGHT OF THE CASTINGS ACCUMULATED AT THE MOUTH OF A SINGLE BURROW. + + +(Weight in ounces given in parenthesis--DP.) + +(1.) Down, Kent (sub-soil red clay, full of flints, over-lying the +chalk). The largest casting which I could find on the flanks of a +steep valley, the sub-soil being here shallow. In this one case, +the casting was not well dried (3.98) + +(2.) Down.--Largest casting which I could find (consisting chiefly +of calcareous matter), on extremely poor pasture land at the bottom +of the valley mentioned under (1.) (3.87) + +(3.) Down.--A large casting, but not of unusual size, from a +nearly level field, poor pasture, laid down in a grass about 35 +years before (1.22) + +(4.) Down. Average weight of 11 not large castings ejected on a +sloping surface on my lawn, after they had suffered some loss of +weight from being exposed during a considerable length of time to +rain (0.7) + +(5.) Near Nice in France.--Average weight of 12 castings of +ordinary dimensions, collected by Dr. King on land which had not +been mown for a long time and where worms abounded, viz., a lawn +protected by shrubberies near the sea; soil sandy and calcareous; +these castings had been exposed for some time to rain, before being +collected, and must have lost some weight by disintegration, but +they still retained their form (1.37) + +(6.) The heaviest of the above twelve castings (1.76) + +(7.) Lower Bengal.--Average weight of 22 castings, collected by +Mr. J. Scott, and stated by him to have been thrown up in the +course of one or two nights (1.24) + +(8.) The heaviest of the above 22 castings (2.09) + +(9.) Nilgiri Mountains, S. India; average weight of the 5 largest +castings collected by Dr. King. They had been exposed to the rain +of the last monsoon, and must have lost some weight (3.15) + +(10.) The heaviest of the above 5 castings (4.34) + + +In this table we see that castings which had been ejected at the +mouth of the same burrow, and which in most cases appeared fresh +and always retained their vermiform configuration, generally +exceeded an ounce in weight after being dried, and sometimes nearly +equalled a quarter of a pound. On the Nilgiri mountains one +casting even exceeded this latter weight. The largest castings in +England were found on extremely poor pasture-land; and these, as +far as I have seen, are generally larger than those on land +producing a rich vegetation. It would appear that worms have to +swallow a greater amount of earth on poor than on rich land, in +order to obtain sufficient nutriment. + +With respect to the tower-like castings near Nice (Nos. 5 and 6 in +the above table), Dr. King often found five or six of them on a +square foot of surface; and these, judging from their average +weight, would have weighed together 7.5 ounces; so that the weight +of those on a square yard would have been 4 lb. 3.5 oz. Dr. King +collected, near the close of the year 1872, all the castings which +still retained their vermiform shape, whether broken down or not, +from a square foot, in a place abounding with worms, on the summit +of a bank, where no castings could have rolled down from above. +These castings must have been ejected, as he judged from their +appearance in reference to the rainy and dry periods near Nice, +within the previous five or six months; they weighed 9.5 oz., or 5 +lb. 5.5 oz. per square yard. After an interval of four months, Dr. +King collected all the castings subsequently ejected on the same +square foot of surface, and they weighed 2.5 oz., or 1 lb. 6.5 oz. +per square yard. Therefore within about ten months, or we will say +for safety's sake within a year, 12 oz. of castings were thrown up +on this one square foot, or 6.75 pounds on the square yard; and +this would give 14.58 tons per acre. + +In a field at the bottom of a valley in the chalk (see No. 2 in the +foregoing table), a square yard was measured at a spot where very +large castings abounded; they appeared, however, almost equally +numerous in a few other places. These castings, which retained +perfectly their vermiform shape, were collected; and they weighed +when partially dried, 1 lb. 13.5 oz. This field had been rolled +with a heavy agricultural roller fifty-two days before, and this +would certainly have flattened every single casting on the land. +The weather had been very dry for two or three weeks before the day +of collection, so that not one casting appeared fresh or had been +recently ejected. We may therefore assume that those which were +weighed had been ejected within, we will say, forty days from the +time when the field was rolled,--that is, twelve days short of the +whole intervening period. I had examined the same part of the +field shortly before it was rolled, and it then abounded with fresh +castings. Worms do not work in dry weather during the summer, or +in winter during severe frosts. If we assume that they work for +only half the year--though this is too low an estimate--then the +worms in this field would eject during the year, 8.387 pounds per +square yard; or 18.12 tons per acre, assuming the whole surface to +be equally productive in castings. + +In the foregoing cases some of the necessary data had to be +estimated, but in the two following cases the results are much more +trustworthy. A lady, on whose accuracy I can implicitly rely, +offered to collect during a year all the castings thrown up on two +separate square yards, near Leith Hill Place, in Surrey. The +amount collected was, however, somewhat less than that originally +ejected by the worms; for, as I have repeatedly observed, a good +deal of the finest earth is washed away, whenever castings are +thrown up during or shortly before heavy rain. Small portions also +adhered to the surrounding blades of grass, and it required too +much time to detach every one of them. + +On sandy soil, as in the present instance, castings are liable to +crumble after dry weather, and particles were thus often lost. The +lady also occasionally left home for a week or two, and at such +times the castings must have suffered still greater loss from +exposure to the weather. These losses were, however, compensated +to some extent by the collections having been made on one of the +squares for four days, and on the other square for two days more +than the year. + +A space was selected (October 9th, 1870) for one of the squares on +a broad, grass-covered terrace, which had been mowed and swept +during many years. It faced the south, but was shaded during part +of the day by trees. It had been formed at least a century ago by +a great accumulation of small and large fragments of sandstone, +together with some sandy earth, rammed down level. It is probable +that it was at first protected by being covered with turf. This +terrace, judging from the number of castings on it, was rather +unfavourable for the existence of worms, in comparison with the +neighbouring fields and an upper terrace. It was indeed surprising +that as many worms could live here as were seen; for on digging a +hole in this terrace, the black vegetable mould together with the +turf was only four inches in thickness, beneath which lay the level +surface of light-coloured sandy soil, with many fragments of +sandstone. Before any castings were collected all the previously +existing ones were carefully removed. The last day's collection +was on October 14th, 1871. The castings were then well dried +before a fire; and they weighed exactly 3.5 lbs. This would give +for an acre of similar land 7.56 tons of dry earth annually ejected +by worms. + +The second square was marked on unenclosed common land, at a height +of about 700 ft. above the sea, at some little distance from Leith +Hill Tower. The surface was clothed with short, fine turf, and had +never been disturbed by the hand of man. The spot selected +appeared neither particularly favourable nor the reverse for worms; +but I have often noticed that castings are especially abundant on +common land, and this may, perhaps, be attributed to the poorness +of the soil. The vegetable mould was here between three and four +inches in thickness. As this spot was at some distance from the +house where the lady lived, the castings were not collected at such +short intervals of time as those on the terrace; consequently the +loss of fine earth during rainy weather must have been greater in +this than in the last case. The castings moreover were more sandy, +and in collecting them during dry weather they sometimes crumbled +into dust, and much was thus lost. Therefore it is certain that +the worms brought up to the surface considerably more earth than +that which was collected. The last collection was made on October +27th, 1871; i.e., 367 days after the square had been marked out and +the surface cleared of all pre-existing castings. The collected +castings, after being well dried, weighed 7.453 pounds; and this +would give, for an acre of the same kind of land, 16.1 tons of +annually ejected dry earth. + + +SUMMARY OF THE FOUR FOREGOING CASES. + + +(1.) Castings ejected near Nice within about a year, collected by +Dr. King on a square foot of surface, calculated to yield per acre +14.58 tons. + +(2.) Castings ejected during about 40 days on a square yard, in a +field of poor pasture at the bottom of a large valley in the Chalk, +calculated to yield annually per acre 18.12 tons. + +(3.) Castings collected from a square yard on an old terrace at +Leith Hill Place, during 369 days, calculated to yield annually per +acre 7.56 tons. + +(4.) Castings collected from a square yard on Leith Hill Common +during 367 days, calculated to yield annually per acre 16.1 tons. + + +The thickness of the layer of mould, which castings ejected during +a year would form if uniformly spread out.--As we know, from the +two last cases in the above summary, the weight of the dried +castings ejected by worms during a year on a square yard of +surface, I wished to learn how thick a layer of ordinary mould this +amount would form if spread uniformly over a square yard. The dry +castings were therefore broken into small particles, and whilst +being placed in a measure were well shaken and pressed down. Those +collected on the Terrace amounted to 124.77 cubic inches; and this +amount, if spread out over a square yard, would make a layer 0.9627 +inch in thickness. Those collected on the Common amounted to +197.56 cubic inches, and would make a similar layer 0.1524 inch in +thickness, + +These thicknesses must, however, be corrected, for the triturated +castings, after being well shaken down and pressed, did not make +nearly so compact a mass as vegetable mould, though each separate +particle was very compact. Yet mould is far from being compact, as +is shown by the number of air-bubbles which rise up when the +surface is flooded with water. It is moreover penetrated by many +fine roots. To ascertain approximately by how much ordinary +vegetable mould would be increased in bulk by being broken up into +small particles and then dried, a thin oblong block of somewhat +argillaceous mould (with the turf pared off) was measured before +being broken up, was well dried and again measured. The drying +caused it to shrink by 1/7 of its original bulk, judging from +exterior measurements alone. It was then triturated and partly +reduced to powder, in the same manner as the castings had been +treated, and its bulk now exceeded (notwithstanding shrinkage from +drying) by 1/16 that of the original block of damp mould. +Therefore the above calculated thickness of the layer, formed by +the castings from the Terrace, after being damped and spread over a +square yard, would have to be reduced by 1/16; and this will reduce +the layer to 0.09 of an inch, so that a layer 0.9 inch in thickness +would be formed in the course of ten years. On the same principle +the castings from the Common would make in the course of a single +year a layer 0.1429 inch, or in the course of 10 years 1.429 inch, +in thickness. We may say in round numbers that the thickness in +the former case would amount to nearly 1 inch, and in the second +case to nearly 1.5 inch in 10 years. + +In order to compare these results with those deduced from the rates +at which small objects left on the surfaces of grass-fields become +buried (as described in the early part of this chapter), we will +give the following summary:- + + +SUMMARY OF THE THICKNESS OF THE MOULD ACCUMULATED OVER OBJECTS LEFT +STREWED ON THE SURFACE, IN THE COURSE OF TEN YEARS. + + +The accumulation of mould during 14.75 years on the surface of a +dry, sandy, grass-field near Maer Hall, amounted to 2.2 inches in +10 years. + +The accumulation during 21.5 years on a swampy field near Maer +Hall, amounted to nearly 1.9 inch in 10 years. + +The accumulation during 7 years on a very swampy field near Maer +Hall amounted to 2.1 inches in 10 years. + +The accumulation during 29 years, on good, argillaceous pasture- +land over the Chalk at Down, amounted to 2.2 inches in 10 years. + +The accumulation during 30 years on the side of a valley over the +Chalk at Down, the soil being argillaceous, very poor, and only +just converted into pasture (so that it was for some years +unfavourable for worms), amounted to 0.83 inch in 10 years. + + +In these cases (excepting the last) it may be seen that the amount +of earth brought to the surface during 10 years is somewhat greater +than that calculated from the castings which were actually weighed. +This excess may be partly accounted for by the loss which the +weighed castings had previously undergone through being washed by +rain, by the adhesion of particles to the blades of the surrounding +grass, and by their crumbling when dry. Nor must we overlook other +agencies which in all ordinary cases add to the amount of mould, +and which would not be included in the castings that were +collected, namely, the fine earth brought up to the surface by +burrowing larvae and insects, especially by ants. The earth +brought up by moles generally has a somewhat different appearance +from vegetable mould; but after a time would not be distinguishable +from it. In dry countries, moreover, the wind plays an important +part in carrying dust from one place to another, and even in +England it must add to the mould on fields near great roads. But +in our country these latter several agencies appear to be of quite +subordinate importance in comparison with the action of worms. + +We have no means of judging how great a weight of earth a single +full-sized worm ejects during a year. Hensen estimates that 53,767 +worms exist in an acre of land; but this is founded on the number +found in gardens, and he believes that only about half as many live +in corn-fields. How many live in old pasture land is unknown; but +if we assume that half the above number, or 26,886 worms live on +such land, then taking from the previous summary 15 tons as the +weight of the castings annually thrown up on an acre of land, each +worm must annually eject 20 ounces. A full-sized casting at the +mouth of a single burrow often exceeds, as we have seen, an ounce +in weight; and it is probable that worms eject more than 20 full- +sized castings during a year. If they eject annually more than 20 +ounces, we may infer that the worms which live in an acre of +pasture land must be less than 26,886 in number. + +Worms live chiefly in the superficial mould, which is usually from +4 or 5 to 10 and even 12 inches in thickness; and it is this mould +which passes over and over again through their bodies and is +brought to the surface. But worms occasionally burrow into the +subsoil to a much greater depth, and on such occasions they bring +up earth from this greater depth; and this process has gone on for +countless ages. Therefore the superficial layer of mould would +ultimately attain, though at a slower and slower rate, a thickness +equal to the depth to which worms ever burrow, were there not other +opposing agencies at work which carry away to a lower level some of +the finest earth which is continually being brought to the surface +by worms. How great a thickness vegetable mould ever attains, I +have not had good opportunities for observing; but in the next +chapter, when we consider the burial of ancient buildings, some +facts will be given on this head. In the two last chapters we +shall see that the soil is actually increased, though only to a +small degree, through the agency of worms; but their chief work is +to sift the finer from the coarser particles, to mingle the whole +with vegetable debris, and to saturate it with their intestinal +secretions. + +Finally, no one who considers the facts given in this chapter--on +the burying of small objects and on the sinking of great stones +left on the surface--on the vast number of worms which live within +a moderate extent of ground on the weight of the castings ejected +from the mouth of the same burrow--on the weight of all the +castings ejected within a known time on a measured space--will +hereafter, as I believe, doubt that worms play an important part in +nature. + + + +CHAPTER IV--THE PART WHICH WORMS HAVE PLAYED IN THE BURIAL OF +ANCIENT BUILDINGS. + + + +The accumulation of rubbish on the sites of great cities +independent of the action of worms--The burial of a Roman villa at +Abinger--The floors and walls penetrated by worms--Subsidence of a +modern pavement--The buried pavement at Beaulieu Abbey--Roman +villas at Chedworth and Brading--The remains of the Roman town at +Silchester--The nature of the debris by which the remains are +covered--The penetration of the tesselated floors and walls by +worms--Subsidence of the floors--Thickness of the mould--The old +Roman city of Wroxeter--Thickness of the mould--Depth of the +foundations of some of the Buildings--Conclusion. + + +Archaeologists are probably not aware how much they owe to worms +for the preservation of many ancient objects. Coins, gold +ornaments, stone implements, &c., if dropped on the surface of the +ground, will infallibly be buried by the castings of worms in a few +years, and will thus be safely preserved, until the land at some +future time is turned up. For instance, many years ago a grass- +field was ploughed on the northern side of the Severn, not far from +Shrewsbury; and a surprising number of iron arrow-heads were found +at the bottom of the furrows, which, as Mr. Blakeway, a local +antiquary, believed, were relics of the battle of Shrewsbury in the +year 1403, and no doubt had been originally left strewed on the +battle-field. In the present chapter I shall show that not only +implements, &c., are thus preserved, but that the floors and the +remains of many ancient buildings in England have been buried so +effectually, in large part through the action of worms, that they +have been discovered in recent times solely through various +accidents. The enormous beds of rubbish, several yards in +thickness, which underlie many cities, such as Rome, Paris, and +London, the lower ones being of great antiquity, are not here +referred to, as they have not been in any way acted on by worms. +When we consider how much matter is daily brought into a great city +for building, fuel, clothing and food, and that in old times when +the roads were bad and the work of the scavenger was neglected, a +comparatively small amount was carried away, we may agree with Elie +de Beaumont, who, in discussing this subject, says, "pour une +voiture de materiaux qui en sort, on y en fait entrer cent." {53} +Nor should we overlook the effects of fires, the demolition of old +buildings, and the removal of rubbish to the nearest vacant space, + +Abinger, Surrey.--Late in the autumn of 1876, the ground in an old +farm-yard at this place was dug to a depth of 2 to 2.5 feet, and +the workmen found various ancient remains. This led Mr. T. H. +Farrer of Abinger Hall to have an adjoining ploughed field +searched. On a trench being dug, a layer of concrete, still partly +covered with tesserae (small red tiles), and surrounded on two +sides by broken-down walls, was soon discovered. It is believed, +{54} that this room formed part of the atrium or reception-room of +a Roman villa. The walls of two or three other small rooms were +afterwards discovered. Many fragments of pottery, other objects, +and coins of several Roman emperors, dating from 133 to 361, and +perhaps to 375 A.D., were likewise found. Also a half-penny of +George I., 1715. The presence of this latter coin seems an +anomaly; but no doubt it was dropped on the ground during the last +century, and since then there has been ample time for its burial +under a considerable depth of the castings of worms. From the +different dates of the Roman coins we may infer that the building +was long inhabited. It was probably ruined and deserted 1400 or +1500 years ago. + +I was present during the commencement of the excavations (August +20, 1877) and Mr. Farrer had two deep trenches dug at opposite ends +of the atrium, so that I might examine the nature of the soil near +the remains. The field sloped from east to west at an angle of +about 7 degrees; and one of the two trenches, shown in the +accompanying section (Fig. 8) was at the upper or eastern end. The +diagram is on a scale of 1/20 of an inch to an inch; but the +trench, which was between 4 and 5 feet broad, and in parts above 5 +feet deep, has necessarily been reduced out of all proportion. The +fine mould over the floor of the atrium varied in thickness from 11 +to 16 inches; and on the side of the trench in the section was a +little over 13 inches. After the mould had been removed, the floor +appeared as a whole moderately level; but it sloped in parts at an +angle of 1 degree, and in one place near the outside at as much as +8 degrees 30 minutes. The wall surrounding the pavement was built +of rough stones, and was 23 inches in thickness where the trench +was dug. Its broken summit was here 13 inches, but in another part +15 inches, beneath the surface of the field, being covered by this +thickness of mould. In one spot, however, it rose to within 6 +inches of the surface. On two sides of the room, where the +junction of the concrete floor with the bounding walls could be +carefully examined, there was no crack or separation. This trench +afterwards proved to have been dug within an adjoining room (11 ft. +by 11 ft. 6 in. in size), the existence of which was not even +suspected whilst I was present. + +On the side of the trench farthest from the buried wall (W), the +mould varied from 9 to 14 inches in thickness; it rested on a mass +(B) 23 inches thick of blackish earth, including many large stones. +Beneath this was a thin bed of very black mould (C), then a layer +of earth full of fragments of mortar (D), and then another thin bed +(about 3 inches thick) (E) of very black mould, which rested on the +undisturbed subsoil (F) of firm, yellowish, argillaceous sand. The +23-inch bed (B) was probably made ground, as this would have +brought up the floor of the room to a level with that of the +atrium. The two thin beds of black mould at the bottom of the +trench evidently marked two former land-surfaces. Outside the +walls of the northern room, many bones, ashes, oyster-shells, +broken pottery and an entire pot were subsequently found at a depth +of 16 inches beneath the surface. + +The second trench was dug on the western or lower side of the +villa: the mould was here only 6.5 inches in thickness, and it +rested on a mass of fine earth full of stones, broken tiles and +fragments of mortar, 34 inches in thickness, beneath which was the +undisturbed sand. Most of this earth had probably been washed down +from the upper part of the field, and the fragments of stones, +tiles, &c., must have come from the immediately adjoining ruins. + +It appears at first sight a surprising fact that this field of +light sandy soil should have been cultivated and ploughed during +many years, and that not a vestige of these buildings should have +been discovered. No one even suspected that the remains of a Roman +villa lay hidden close beneath the surface. But the fact is less +surprising when it is known that the field, as the bailiff +believed, had never been ploughed to a greater depth than 4 inches. +It is certain that when the land was first ploughed, the pavement +and the surrounding broken walls must have been covered by at least +4 inches of soil, for otherwise the rotten concrete floor would +have been scored by the ploughshare, the tesserae torn up, and the +tops of the old walls knocked down. + +When the concrete and tesserae were first cleared over a space of +14 by 9 ft., the floor which was coated with trodden-down earth +exhibited no signs of having been penetrated by worms; and although +the overlying fine mould closely resembled that which in many +places has certainly been accumulated by worms, yet it seemed +hardly possible that this mould could have been brought up by worms +from beneath the apparently sound floor. It seemed also extremely +improbable that the thick walls, surrounding the room and still +united to the concrete, had been undermined by worms, and had thus +been caused to sink, being afterwards covered up by their castings. +I therefore at first concluded that all the fine mould above the +ruins had been washed down from the upper parts of the field; but +we shall soon see that this conclusion was certainly erroneous, +though much fine earth is known to be washed down from the upper +part of the field in its present ploughed state during heavy rains. + +Although the concrete floor did not at first appear to have been +anywhere penetrated by worms, yet by the next morning little cakes +of the trodden-down earth had been lifted up by worms over the +mouths of seven burrows, which passed through the softer parts of +the naked concrete, or between the interstices of the tesserae. On +the third morning twenty-five burrows were counted; and by suddenly +lifting up the little cakes of earth, four worms were seen in the +act of quickly retreating. Two castings were thrown up during the +third night on the floor, and these were of large size. The season +was not favourable for the full activity of worms, and the weather +had lately been hot and dry, so that most of the worms now lived at +a considerable depth. In digging the two trenches many open +burrows and some worms were encountered at between 30 and 40 inches +beneath the surface; but at a greater depth they became rare. One +worm, however, was cut through at 48.5, and another at 51.5 inches +beneath the surface. A fresh humus-lined burrow was also met with +at a depth of 57 and another at 65.5 inches. At greater depths +than this, neither burrows nor worms were seen. + +As I wished to learn how many worms lived beneath the floor of the +atrium--a space of about 14 by 9 feet--Mr. Farrer was so kind as to +make observations for me, during the next seven weeks, by which +time the worms in the surrounding country were in full activity, +and were working near the surface. It is very improbable that +worms should have migrated from the adjoining field into the small +space of the atrium, after the superficial mould in which they +prefer to live, had been removed. We may therefore conclude that +the burrows and the castings which were seen here during the +ensuing seven weeks were the work of the former inhabitants of the +space. I will now give a few extracts from Mr. Farrer's notes. + +Aug. 26th, 1877; that is, five days after the floor had been +cleared. On the previous night there had been some heavy rain, +which washed the surface clean, and now the mouths of forty burrows +were counted. Parts of the concrete were seen to be solid, and had +never been penetrated by worms, and here the rain-water lodged. + +Sept. 5th.--Tracks of worms, made during the previous night, could +be seen on the surface of the floor, and five or six vermiform +castings had been thrown up. These were defaced. + +Sept. 12th.--During the last six days, the worms have not been +active, though many castings have been ejected in the neighbouring +fields; but on this day the earth was a little raised over the +mouths of the burrows, or castings were ejected, at ten fresh +points. These were defaced. It should be understood that when a +fresh burrow is spoken of, this generally means only that an old +burrow has been re-opened. Mr. Farrer was repeatedly struck with +the pertinacity with which the worms re-opened their old burrows, +even when no earth was ejected from them. I have often observed +the same fact, and generally the mouths of the burrows are +protected by an accumulation of pebbles, sticks or leaves. Mr. +Farrer likewise observed that the worms living beneath the floor of +the atrium often collected coarse grains of sand, and such little +stones as they could find, round the mouths of their burrows. + +Sept. 13th; soft wet weather. The mouths of the burrows were re- +opened, or castings were ejected, at 31 points; these were all +defaced. + +Sept. 14th; 34 fresh holes or castings; all defaced. + +Sept. 15th; 44 fresh holes, only 5 castings; all defaced. + +Sept. 18th; 43 fresh holes, 8 castings; all defaced. + +The number of castings on the surrounding fields was now very +large. + +Sept. 19th; 40 holes, 8 castings; all defaced. + +Sept. 22nd; 43 holes, only a few fresh castings; all defaced. + +Sept. 23rd; 44 holes, 8 castings. + +Sept. 25th; 50 holes, no record of the number of castings. + +Oct. 13th; 61 holes, no record of the number of castings. + +After an interval of three years, Mr. Farrer, at my request, again +looked at the concrete floor, and found the worms still at work. + +Knowing what great muscular power worms possess, and seeing how +soft the concrete was in many parts, I was not surprised at its +having been penetrated by their burrows; but it is a more +surprising fact that the mortar between the rough stones of the +thick walls, surrounding the rooms, was found by Mr. Farrer to have +been penetrated by worms. On August 26th, that is, five days after +the ruins had been exposed, he observed four open burrows on the +broken summit of the eastern wall (W in Fig. 8); and, on September +15th, other burrows similarly situated were seen. It should also +be noted that in the perpendicular side of the trench (which was +much deeper than is represented in Fig. 8) three recent burrows +were seen, which ran obliquely far down beneath the base of the old +wall. + +We thus see that many worms lived beneath the floor and the walls +of the atrium at the time when the excavations were made; and that +they afterwards almost daily brought up earth to the surface from a +considerable depth. There is not the slightest reason to doubt +that worms have acted in this manner ever since the period when the +concrete was sufficiently decayed to allow them to penetrate it; +and even before that period they would have lived beneath the +floor, as soon as it became pervious to rain, so that the soil +beneath was kept damp. The floor and the walls must therefore have +been continually undermined; and fine earth must have been heaped +on them during many centuries, perhaps for a thousand years. If +the burrows beneath the floor and walls, which it is probable were +formerly as numerous as they now are, had not collapsed in the +course of time in the manner formerly explained, the underlying +earth would have been riddled with passages like a sponge; and as +this was not the case, we may feel sure that they have collapsed. +The inevitable result of such collapsing during successive +centuries, will have been the slow subsidence of the floor and of +the walls, and their burial beneath the accumulated worm-castings. +The subsidence of a floor, whilst it still remains nearly +horizontal, may at first appear improbable; but the case presents +no more real difficulty than that of loose objects strewed on the +surface of a field, which, as we have seen, become buried several +inches beneath the surface in the course of a few years, though +still forming a horizontal layer parallel to the surface. The +burial of the paved and level path on my lawn, which took place +under my own observation, is an analogous case. Even those parts +of the concrete floor which the worms could not penetrate would +almost certainly have been undermined, and would have sunk, like +the great stones at Leith Hill Place and Stonehenge, for the soil +would have been damp beneath them. But the rate of sinking of the +different parts would not have been quite equal, and the floor was +not quite level. The foundations of the boundary walls lie, as +shown in the section, at a very small depth beneath the surface; +they would therefore have tended to subside at nearly the same rate +as the floor. But this would not have occurred if the foundations +had been deep, as in the case of some other Roman ruins presently +to be described. + +Finally, we may infer that a large part of the fine vegetable +mould, which covered the floor and the broken-down walls of this +villa, in some places to a thickness of 16 inches, was brought up +from below by worms. From facts hereafter to be given there can be +no doubt that some of the finest earth thus brought up will have +been washed down the sloping surface of the field during every +heavy shower of rain. If this had not occurred a greater amount of +mould would have accumulated over the ruins than that now present. +But beside the castings of worms and some earth brought up by +insects, and some accumulation of dust, much fine earth will have +been washed over the ruins from the upper parts of the field, since +it has been under cultivation; and from over the ruins to the lower +parts of the slope; the present thickness of the mould being the +resultant of these several agencies. + + +I may here append a modern instance of the sinking of a pavement, +communicated to me in 1871 by Mr. Ramsay, Director of the +Geological Survey of England. A passage without a roof, 7 feet in +length by 3 feet 2 inches in width, led from his house into the +garden, and was paved with slabs of Portland stone. Several of +these slabs were 16 inches square, others larger, and some a little +smaller. This pavement had subsided about 3 inches along the +middle of the passage, and two inches on each side, as could be +seen by the lines of cement by which the slabs had been originally +joined to the walls. The pavement had thus become slightly concave +along the middle; but there was no subsidence at the end close to +the house. Mr. Ramsay could not account for this sinking, until he +observed that castings of black mould were frequently ejected along +the lines of junction between the slabs; and these castings were +regularly swept away. The several lines of junction, including +those with the lateral walls, were altogether 39 feet 2 inches in +length. The pavement did not present the appearance of ever having +been renewed, and the house was believed to have been built about +eighty-seven years ago. Considering all these circumstances, Mr. +Ramsay does not doubt that the earth brought up by the worms since +the pavement was first laid down, or rather since the decay of the +mortar allowed the worms to burrow through it, and therefore within +a much shorter time than the eighty-seven years, has sufficed to +cause the sinking of the pavement to the above amount, except close +to the house, where the ground beneath would have been kept nearly +dry. + +Beaulieu Abbey, Hampshire.--This abbey was destroyed by Henry +VIII., and there now remains only a portion of the southern aisle- +wall. It is believed that the king had most of the stones carried +away for building a castle; and it is certain that they have been +removed. The positions of the nave and transepts were ascertained +not long ago by the foundations having been found; and the place is +now marked by stones let into the ground. Where the abbey formerly +stood, there now extends a smooth grass-covered surface, which +resembles in all respects the rest of the field. The guardian, a +very old man, said the surface had never been levelled in his time. +In the year 1853, the Duke of Buccleuch had three holes dug in the +turf within a few yards of one another, at the western end of the +nave; and the old tesselated pavement of the abbey was thus +discovered. These holes were afterwards surrounded by brickwork, +and protected by trap-doors, so that the pavement might be readily +inspected and preserved. When my son William examined the place on +January 5, 1872, he found that the pavement in the three holes lay +at depths of 6.75, 10 and 11.5 inches beneath the surrounding turf- +covered surface. The old guardian asserted that he was often +forced to remove worm-castings from the pavement; and that he had +done so about six months before. My son collected all from one of +the holes, the area of which was 5.32 square feet, and they weighed +7.97 ounces. Assuming that this amount had accumulated in six +months, the accumulation during a year on a square yard would be +1.68 pounds, which, though a large amount, is very small compared +with what, as we have seen, is often ejected on fields and commons. +When I visited the abbey on June 22, 1877, the old man said that he +had cleared out the holes about a month before, but a good many +castings had since been ejected. I suspect that he imagined that +he swept the pavements oftener than he really did, for the +conditions were in several respects very unfavourable for the +accumulation of even a moderate amount of castings. The tiles are +rather large, viz., about 5.5 inches square, and the mortar between +them was in most places sound, so that the worms were able to bring +up earth from below only at certain points. The tiles rested on a +bed of concrete, and the castings in consequence consisted in large +part (viz., in the proportion of 19 to 33) of particles of mortar, +grains of sand, little fragments of rock, bricks or tile; and such +substances could hardly be agreeable, and certainly not nutritious, +to worms. + +My son dug holes in several places within the former walls of the +abbey, at a distance of several yards from the above described +bricked squares. He did not find any tiles, though these are known +to occur in some other parts, but he came in one spot to concrete +on which tiles had once rested. The fine mould beneath the turf on +the sides of the several holes, varied in thickness from only 2 to +2.75 inches, and this rested on a layer from 8.75 to above 11 +inches in thickness, consisting of fragments of mortar and stone- +rubbish with the interstices compactly filled up with black mould. +In the surrounding field, at a distance of 20 yards from the abbey, +the fine vegetable mould was 11 inches thick. + +We may conclude from these facts that when the abbey was destroyed +and the stones removed, a layer of rubbish was left over the whole +surface, and that as soon as the worms were able to penetrate the +decayed concrete and the joints between the tiles, they slowly +filled up the interstices in the overlying rubbish with their +castings, which were afterwards accumulated to a thickness of +nearly three inches over the whole surface. If we add to this +latter amount the mould between the fragments of stones, some five +or six inches of mould must have been brought up from beneath the +concrete or tiles. The concrete or tiles will consequently have +subsided to nearly this amount. The bases of the columns of the +aisles are now buried beneath mould and turf. It is not probable +that they can have been undermined by worms, for their foundations +would no doubt have been laid at a considerable depth. If they +have not subsided, the stones of which the columns were constructed +must have been removed from beneath the former level of the floor. + +Chedworth, Gloucestershire.--The remains of a large Roman villa +were discovered here in 1866, on ground which had been covered with +wood from time immemorial. No suspicion seems ever to have been +entertained that ancient buildings lay buried here, until a +gamekeeper, in digging for rabbits, encountered some remains. {55} +But subsequently the tops of some stone walls were detected in +parts of the wood, projecting a little above the surface of the +ground. Most of the coins found here belonged to Constans (who +died 350 A.D.) and the Constantine family. My sons Francis and +Horace visited the place in November 1877, for the sake of +ascertaining what part worms may have played in the burial of these +extensive remains. But the circumstances were not favourable for +this object, as the ruins are surrounded on three sides by rather +steep banks, down which earth is washed during rainy weather. +Moreover most of the old rooms have been covered with roofs, for +the protection of the elegant tesselated pavements. + +A few facts may, however, be given on the thickness of the soil +over these ruins. Close outside the northern rooms there is a +broken wall, the summit of which was covered by 5 inches of black +mould; and in a hole dug on the outer side of this wall, where the +ground had never before been disturbed, black mould, full of +stones, 26 inches in thickness, was found, resting on the +undisturbed sub-soil of yellow clay. At a depth of 22 inches from +the surface a pig's jaw and a fragment of a tile were found. When +the excavations were first made, some large trees grew over the +ruins; and the stump of one has been left directly over a party- +wall near the bath-room, for the sake of showing the thickness of +the superincumbent soil, which was here 38 inches. In one small +room, which, after being cleared out, had not been roofed over, my +sons observed the hole of a worm passing through the rotten +concrete, and a living worm was found within the concrete. In +another open room worm-castings were seen on the floor, over which +some earth had by this means been deposited, and here grass now +grew. + +Brading, Isle of Wight.--A fine Roman villa was discovered here in +1880; and by the end of October no less than 18 chambers had been +more or less cleared. A coin dated 337 A.D. was found. My son +William visited the place before the excavations were completed; +and he informs me that most of the floors were at first covered +with much rubbish and fallen stones, having their interstices +completely filled up with mould, abounding, as the workmen said, +with worms, above which there was mould without any stones. The +whole mass was in most places from 3 to above 4 ft. in thickness. +In one very large room the overlying earth was only 2 ft. 6 in. +thick; and after this had been removed, so many castings were +thrown up between the tiles that the surface had to be almost daily +swept. Most of the floors were fairly level. The tops of the +broken-down walls were covered in some places by only 4 or 5 inches +of soil, so that they were occasionally struck by the plough, but +in other places they were covered by from 13 to 18 inches of soil. +It is not probable that these walls could have been undermined by +worms and subsided, as they rested on a foundation of very hard red +sand, into which worms could hardly burrow. The mortar, however, +between the stones of the walls of a hypocaust was found by my son +to have been penetrated by many worm-burrows. The remains of this +villa stand on land which slopes at an angle of about 3 degrees; +and the land appears to have been long cultivated. Therefore no +doubt a considerable quantity of fine earth has been washed down +from the upper parts of the field, and has largely aided in the +burial of these remains. + +Silchester, Hampshire.--The ruins of this small Roman town have +been better preserved than any other remains of the kind in +England. A broken wall, in most parts from 15 to 18 feet in height +and about 1.5 mile in compass, now surrounds a space of about 100 +acres of cultivated land, on which a farm-house and a church stand. +{56} Formerly, when the weather was dry, the lines of the buried +walls could be traced by the appearance of the crops; and recently +very extensive excavations have been undertaken by the Duke of +Wellington, under the superintendence of the late Rev. J. G. Joyce, +by which means many large buildings have been discovered. Mr. +Joyce made careful coloured sections, and measured the thickness of +each bed of rubbish, whilst the excavations were in progress; and +he has had the kindness to send me copies of several of them. When +my sons Francis and Horace visited these ruins, he accompanied +them, and added his notes to theirs. + +Mr. Joyce estimates that the town was inhabited by the Romans for +about three centuries; and no doubt much matter must have +accumulated within the walls during this long period. It appears +to have been destroyed by fire, and most of the stones used in the +buildings have since been carried away. These circumstances are +unfavourable for ascertaining the part which worms have played in +the burial of the ruins; but as careful sections of the rubbish +overlying an ancient town have seldom or never before been made in +England, I will give copies of the most characteristic portions of +some of those made by Mr. Joyce. They are of too great length to +be here introduced entire. + +An east and west section, 30 ft. in length, was made across a room +in the Basilica, now called the Hall of the Merchants (Fig. 9). +The hard concrete floor, still covered here and there with +tesserae, was found at 3 ft. beneath the surface of the field, +which was here level. On the floor there were two large piles of +charred wood, one alone of which is shown in the part of the +section here given. This pile was covered by a thin white layer of +decayed stucco or plaster, above which was a mass, presenting a +singularly disturbed appearance, of broken tiles, mortar, rubbish +and fine gravel, together 27 inches in thickness. Mr. Joyce +believes that the gravel was used in making the mortar or concrete, +which has since decayed, some of the lime probably having been +dissolved. The disturbed state of the rubbish may have been due to +its having been searched for building stones. This bed was capped +by fine vegetable mould, 9 inches in thickness. From these facts +we may conclude that the Hall was burnt down, and that much rubbish +fell on the floor, through and from which the worms slowly brought +up the mould, now forming the surface of the level field. + +A section across the middle of another hall in the Basilica, 32 +feet 6 inches in length, called the AErarium, is shown in Fig. 10. +It appears that we have here evidence of two fires, separated by an +interval of time, during which the 6 inches of "mortar and concrete +with broken tiles" was accumulated. Beneath one of the layers of +charred wood, a valuable relic, a bronze eagle, was found; and this +shows that the soldiers must have deserted the place in a panic. +Owing to the death of Mr. Joyce, I have not been able to ascertain +beneath which of the two layers the eagle was found. The bed of +rubble overlying the undisturbed gravel originally formed, as I +suppose, the floor, for it stands on a level with that of a +corridor, outside the walls of the Hall; but the corridor is not +shown in the section as here given. The vegetable mould was 16 +inches thick in the thickest part; and the depth from the surface +of the field, clothed with herbage, to the undisturbed gravel, was +40 inches. + +The section shown in Fig. 11 represents an excavation made in the +middle of the town, and is here introduced because the bed of "rich +mould" attained, according to Mr. Joyce, the unusual thickness of +20 inches. Gravel lay at the depth of 48 inches from the surface; +but it was not ascertained whether this was in its natural state, +or had been brought here and had been rammed down, as occurs in +some other places. + +The section shown in Fig. 12 was taken in the centre of the +Basilica, and though it was 5 feet in depth, the natural sub-soil +was not reached. The bed marked "concrete" was probably at one +time a floor; and the beds beneath seem to be the remnants of more +ancient buildings. The vegetable mould was here only 9 inches +thick. In some other sections, not copied, we likewise have +evidence of buildings having been erected over the ruins of older +ones. In one case there was a layer of yellow clay of very unequal +thickness between two beds of debris, the lower one of which rested +on a floor with tesserae. The ancient broken walls appear to have +been sometimes roughly cut down to a uniform level, so as to serve +as the foundations for a temporary building; and Mr. Joyce suspects +that some of these buildings were wattled sheds, plastered with +clay, which would account for the above-mentioned layer of clay. + +Turning now to the points which more immediately concern us. Worm- +castings were observed on the floors of several of the rooms, in +one of which the tesselation was unusually perfect. The tesserae +here consisted of little cubes of hard sandstone of about 1 inch, +several of which were loose or projected slightly above the general +level. One or occasionally two open worm-burrows were found +beneath all the loose tesserae. Worms have also penetrated the old +walls of these ruins. A wall, which had just been exposed to view +during the excavations then in progress, was examined; it was built +of large flints, and was 18 inches in thickness. It appeared +sound, but when the soil was removed from beneath, the mortar in +the lower part was found to be so much decayed that the flints fell +apart from their own weight. Here, in the middle of the wall, at a +depth of 29 inches beneath the old floor and of 49.5 inches beneath +the surface of the field, a living worm was found, and the mortar +was penetrated by several burrows. + +A second wall was exposed to view for the first time, and an open +burrow was seen on its broken summit. By separating the flints +this burrow was traced far down in the interior of the wall; but as +some of the flints cohered firmly, the whole mass was disturbed in +pulling down the wall, and the burrow could not be traced to the +bottom. The foundations of a third wall, which appeared quite +sound, lay at a depth of 4 feet beneath one of the floors, and of +course at a considerably greater depth beneath the level of the +ground. A large flint was wrenched out of the wall at about a foot +from the base, and this required much force, as the mortar was +sound; but behind the flint in the middle of the wall, the mortar +was friable, and here there were worm-burrows. Mr. Joyce and my +sons were surprised at the blackness of the mortar in this and in +several other cases, and at the presence of mould in the interior +of the walls. Some may have been placed there by the old builders +instead of mortar; but we should remember that worms line their +burrows with black humus. Moreover open spaces would almost +certainly have been occasionally left between the large irregular +flints; and these spaces, we may feel sure, would be filled up by +the worms with their castings, as soon as they were able to +penetrate the wall. Rain-water, oozing down the burrows would also +carry fine dark-coloured particles into every crevice. Mr. Joyce +was at first very sceptical about the amount of work which I +attributed to worms; but he ends his notes with reference to the +last-mentioned wall by saying, "This case caused me more surprise +and brought more conviction to me than any other. I should have +said, and did say, that it was quite impossible such a wall could +have been penetrated by earth-worms." + +In almost all the rooms the pavement has sunk considerably, +especially towards the middle; and this is shown in the three +following sections. The measurements were made by stretching a +string tightly and horizontally over the floor. The section, Fig. +13, was taken from north to south across a room, 18 feet 4 inches +in length, with a nearly perfect pavement, next to the "Red Wooden +Hut." In the northern half, the subsidence amounted to 5.75 inches +beneath the level of the floor as it now stands close to the walls; +and it was greater in the northern than in the southern half; but, +according to Mr. Joyce, the entire pavement has obviously subsided. +In several places, the tesserae appeared as if drawn a little away +from the walls; whilst in other places they were still in close +contact with them. + +In Fig. 14, we see a section across the paved floor of the southern +corridor or ambulatory of a quadrangle, in an excavation made near +"The Spring." The floor is 7 feet 9 inches wide, and the broken- +down walls now project only 0.75 of an inch above its level. The +field, which was in pasture, here sloped from north to south, at an +angle of 30 degrees, 40 seconds. The nature of the ground at some +little distance on each side of the corridor is shown in the +section. It consisted of earth full of stones and other debris, +capped with dark vegetable mould which was thicker on the lower or +southern than on the northern side. The pavement was nearly level +along lines parallel to the side-walls, but had sunk in the middle +as much as 7.75 inches. + +A small room at no great distance from that represented in Fig. 13, +had been enlarged by the Roman occupier on the southern side, by an +addition of 5 feet 4 inches in breadth. For this purpose the +southern wall of the house had been pulled down, but the +foundations of the old wall had been left buried at a little depth +beneath the pavement of the enlarged room. Mr. Joyce believes that +this buried wall must have been built before the reign of Claudius +II., who died 270 A.D. We see in the accompanying section, Fig. +15, that the tesselated pavement has subsided to a less degree over +the buried wall than elsewhere; so that a slight convexity or +protuberance here stretched in a straight line across the room. +This led to a hole being dug, and the buried wall was thus +discovered. + +We see in these three sections, and in several others not given, +that the old pavements have sunk or sagged considerably. Mr. Joyce +formerly attributed this sinking solely to the slow settling of the +ground. That there has been some settling is highly probable, and +it may be seen in Fig. 15 that the pavement for a width of 5 feet +over the southern enlargement of the room, which must have been +built on fresh ground, has sunk a little more than on the old +northern side. But this sinking may possibly have had no +connection with the enlargement of the room; for in Fig. 13 one +half of the pavement has subsided more than the other half without +any assignable cause. In a bricked passage to Mr. Joyce's own +house, laid down only about six years ago, the same kind of sinking +has occurred as in the ancient buildings. Nevertheless it does not +appear probable that the whole amount of sinking can be thus +accounted for. The Roman builders excavated the ground to an +unusual depth for the foundations of their walls, which were thick +and solid; it is therefore hardly credible that they should have +been careless about the solidity of the bed on which their +tesselated and often ornamented pavements were laid. The sinking +must, as it appears to me, be attributed in chief part to the +pavement having been undermined by worms, which we know are still +at work. Even Mr. Joyce at last admitted that this could not have +failed to have produced a considerable effect. Thus also the large +quantity of fine mould overlying the pavements can be accounted +for, the presence of which would otherwise be inexplicable. My +sons noticed that in one room in which the pavement had sagged very +little, there was an unusually small amount of overlying mould. + +As the foundations of the walls generally lie at a considerable +depth, they will either have not subsided at all through the +undermining action of worms, or they will have subsided much less +than the floor. This latter result would follow from worms not +often working deep down beneath the foundations; but more +especially from the walls not yielding when penetrated by worms, +whereas the successively formed burrows in a mass of earth, equal +to one of the walls in depth and thickness, would have collapsed +many times since the desertion of the ruins, and would consequently +have shrunk or subsided. As the walls cannot have sunk much or at +all, the immediately adjoining pavement from adhering to them will +have been prevented from subsiding; and thus the present curvature +of the pavement is intelligible. + +The circumstance which has surprised me most with respect to +Silchester is that during the many centuries which have elapsed +since the old buildings were deserted, the vegetable mould has not +accumulated over them to a greater thickness than that here +observed. In most places it is only about 9 inches in thickness, +but in some places 12 or even more inches. In Fig. 11, it is given +as 20 inches, but this section was drawn by Mr. Joyce before his +attention was particularly called to this subject. The land +enclosed within the old walls is described as sloping slightly to +the south; but there are parts which, according to Mr. Joyce, are +nearly level, and it appears that the mould is here generally +thicker than elsewhere. The surface slopes in other parts from +west to east, and Mr. Joyce describes one floor as covered at the +western end by rubbish and mould to a thickness of 28.5 inches, and +at the eastern end by a thickness of only 11.5 inches. A very +slight slope suffices to cause recent castings to flow downwards +during heavy rain, and thus much earth will ultimately reach the +neighbouring rills and streams and be carried away. By this means, +the absence of very thick beds of mould over these ancient ruins +may, as I believe, be explained. Moreover most of the land here +has long been ploughed, and this would greatly aid the washing away +of the finer earth during rainy weather. + +The nature of the beds immediately beneath the vegetable mould in +some of the sections is rather perplexing. We see, for instance, +in the section of an excavation in a grass meadow (Fig. 14), which +sloped from north to south at an angle of 30 degrees 40 seconds, +that the mould on the upper side is only six inches and on the +lower side nine inches in thickness. But this mould lies on a mass +(25.5 inches in thickness on the upper side) "of dark brown mould," +as described by Mr. Joyce, "thickly interspersed with small pebbles +and bits of tiles, which present a corroded or worn appearance. +The state of this dark-coloured earth is like that of a field which +has long been ploughed, for the earth thus becomes intermingled +with stones and fragments of all kinds which have been much exposed +to the weather. If during the course of many centuries this grass +meadow and the other now cultivated fields have been at times +ploughed, and at other times left as pasture, the nature of the +ground in the above section is rendered intelligible. For worms +will continually have brought up fine earth from below, which will +have been stirred up by the plough whenever the land was +cultivated. But after a time a greater thickness of fine earth +will thus have been accumulated than could be reached by the +plough; and a bed like the 25.5-inch mass, in Fig. 14, will have +been formed beneath the superficial mould, which latter will have +been brought to the surface within more recent times, and have been +well sifted by the worms. + +Wroxeter, Shropshire. --The old Roman city of Uriconium was founded +in the early part of the second century, if not before this date; +and it was destroyed, according to Mr. Wright, probably between the +middle of the fourth and fifth century. The inhabitants were +massacred, and skeletons of women were found in the hypocausts. +Before the year 1859, the sole remnant of the city above ground, +was a portion of a massive wall about 20 ft. in height. The +surrounding land undulates slightly, and has long been under +cultivation. It had been noticed that the corn-crops ripened +prematurely in certain narrow lines, and that the snow remained +unmelted in certain places longer than in others. These +appearances led, as I was informed, to extensive excavations being +undertaken. The foundations of many large buildings and several +streets have thus been exposed to view. The space enclosed within +the old walls is an irregular oval, about 1 mile in length. Many +of the stones or bricks used in the buildings must have been +carried away; but the hypocausts, baths, and other underground +buildings were found tolerably perfect, being filled with stones, +broken tiles, rubbish and soil. The old floors of various rooms +were covered with rubble. As I was anxious to know how thick the +mantle of mould and rubbish was, which had so long concealed these +ruins, I applied to Dr. H. Johnson, who had superintended the +excavations; and he, with the greatest kindness, twice visited the +place to examine it in reference to my questions, and had many +trenches dug in four fields which had hitherto been undisturbed. +The results of his observations are given in the following Table. +He also sent me specimens of the mould, and answered, as far as he +could, all my questions. + + +MEASUREMENTS BY DR. H. JOHNSON OF THE THICKNESS OF THE VEGETABLE +MOULD OVER THE ROMAN RUINS AT WROXETER. + + +Trenches dug in a field called "Old Works." + +(Thickness of mould in inches shown in parenthesis--DP.) + +1. At a depth of 36 inches undisturbed sand was reached (20) + +2. At a depth of 33 inches concrete was reached (21) + +3. At a depth of 9 inches concrete was reached (9) + +Trenches dug in a field called "Shop Leasows;" this is the highest +field within the old walls, and slopes down from a sub-central +point on all sides at about an angle of 2 degrees. + +4. Summit of field, trench 45 inches deep (40) + +5. Close to summit of field, trench 36 inches deep (26) + +6. Close to summit of field, trench 28 inches deep (28) + +7. Near summit of field, trench 36 inches deep (24) + +8. Near summit of field, trench at one end 39 inches deep; the +mould here graduated into the underlying undisturbed sand, and its +thickness (24 inches) is somewhat arbitrary. At the other end of +the trench, a causeway was encountered at a depth of only 7 inches, +and the mould was here only 7 inches thick (24) + +9. Trench close to the last, 28 inches in depth (24) + +10. Lower part of same field, trench 30 inches deep (15) + +11. Lower part of same field, trench 31 inches deep (17) + +12. Lower part of same field, trench 36 inches deep, at which +depth undisturbed sand was reached (28) + +13. In another part of same field, trench 9.5 inches deep stopped +by concrete (9.5) + +14. In another part of same field, trench 9 inches deep, stopped +by concrete (9) + +15. In another part of the same field, trench 24 inches deep, when +sand was reached (16) + +16. In another part of same field, trench 30 inches deep, when +stones were reached; at one end of the trench mould 12 inches, at +the other end 14 inches thick (13) + +Small field between "Old Works" and "Shop Leasows," I believe +nearly as high as the upper part of the latter field. + +17. Trench 26 inches deep (24) + +18. Trench 10 inches deep, and then came upon a causeway (10) + +19. Trench 34 inches deep (30) + +20. Trench 31 inches deep (31) + +Field on the western side of the space enclosed within the old +walls. + +21. Trench 28 inches deep, when undisturbed sand was reached (16) + +22. Trench 29 inches deep, when undisturbed sand was reached (15) + +23. Trench 14 inches deep, and then came upon a building (14) + + +Dr. Johnson distinguished as mould the earth which differed, more +or less abruptly, in its dark colour and in its texture from the +underlying sand or rubble. In the specimens sent to me, the mould +resembled that which lies immediately beneath the turf in old +pasture-land, excepting that it often contained small stones, too +large to have passed through the bodies of worms. But the trenches +above described were dug in fields, none of which were in pasture, +and all had been long cultivated. Bearing in mind the remarks made +in reference to Silchester on the effects of long-continued +culture, combined with the action of worms in bringing up the finer +particles to the surface, the mould, as so designated by Dr. +Johnson, seems fairly well to deserve its name. Its thickness, +where there was no causeway, floor or walls beneath, was greater +than has been elsewhere observed, namely, in many places above 2 +ft., and in one spot above 3 ft. The mould was thickest on and +close to the nearly level summit of the field called "Shop +Leasows," and in a small adjoining field, which, as I believe, is +of nearly the same height. One side of the former field slopes at +an angle of rather above 2 degrees, and I should have expected that +the mould, from being washed down during heavy rain, would have +been thicker in the lower than in the upper part; but this was not +the case in two out of the three trenches here dug. + +In many places, where streets ran beneath the surface, or where old +buildings stood, the mould was only 8 inches in thickness; and Dr. +Johnson was surprised that in ploughing the land, the ruins had +never been struck by the plough as far as he had heard. He thinks +that when the land was first cultivated the old walls were perhaps +intentionally pulled down, and that hollow places were filled up. +This may have been the case; but if after the desertion of the city +the land was left for many centuries uncultivated, worms would have +brought up enough fine earth to have covered the ruins completely; +that is if they had subsided from having been undermined. The +foundations of some of the walls, for instance those of the portion +still standing about 20 feet above the ground, and those of the +marketplace, lie at the extraordinary depth of 14 feet; but it is +highly improbable that the foundations were generally so deep. The +mortar employed in the buildings must have been excellent, for it +is still in parts extremely hard. Wherever walls of any height +have been exposed to view, they are, as Dr. Johnson believes, +still perpendicular. The walls with such deep foundations cannot +have been undermined by worms, and therefore cannot have subsided, +as appears to have occurred at Abinger and Silchester. Hence it is +very difficult to account for their being now completely covered +with earth; but how much of this covering consists of vegetable +mould and how much of rubble I do not know. The market-place, with +the foundations at a depth of 14 feet, was covered up, as Dr. +Johnson believes, by between 6 and 24 inches of earth. The tops of +the broken-down walls of a caldarium or bath, 9 feet in depth, were +likewise covered up with nearly 2 feet of earth. The summit of an +arch, leading into an ash-pit 7 feet in depth, was covered up with +not more than 8 inches of earth. Whenever a building which has not +subsided is covered with earth, we must suppose, either that the +upper layers of stone have been at some time carried away by man, +or that earth has since been washed down during heavy rain, or +blown down during storms, from the adjoining land; and this would +be especially apt to occur where the land has long been cultivated. +In the above cases the adjoining land is somewhat higher than the +three specified sites, as far as I can judge by maps and from +information given me by Dr. Johnson. If; however, a great pile of +broken stones, mortar, plaster, timber and ashes fell over the +remains of any building, their disintegration in the course of +time, and the sifting action of worms, would ultimately conceal the +whole beneath fine earth. + +Conclusion. --The cases given in this chapter show that worms have +played a considerable part in the burial and concealment of several +Roman and other old buildings in England; but no doubt the washing +down of soil from the neighbouring higher lands, and the deposition +of dust, have together aided largely in the work of concealment. +Dust would be apt to accumulate wherever old broken-down walls +projected a little above the then existing surface and thus +afforded some shelter. The floors of the old rooms, halls and +passages have generally sunk, partly from the settling of the +ground, but chiefly from having been undermined by worms; and the +sinking has commonly been greater in the middle than near the +walls. The walls themselves, whenever their foundations do not lie +at a great depth, have been penetrated and undermined by worms, and +have consequently subsided. The unequal subsidence thus caused, +probably explains the great cracks which may be seen in many +ancient walls, as well as their inclination from the perpendicular. + + + +CHAPTER V--THE ACTION OF WORMS IN THE DENUDATION OF THE LAND. + + + +Evidence of the amount of denudation which the land has undergone-- +Sub-aerial denudation--The deposition of dust--Vegetable mould, its +dark colour and fine texture largely due to the action of worms-- +The disintegration of rocks by the humus-acids --Similar acids +apparently generated within the bodies of worms--The action of +these acids facilitated by the continued movement of the particles +of earth--A thick bed of mould checks the disintegration of the +underlying soil and rocks. Particles of stone worn or triturated +in the gizzards of worms--Swallowed stones serve as mill-stones-- +The levigated state of the castings--Fragments of brick in the +castings over ancient buildings well rounded. The triturating +power of worms not quite insignificant under a geological point of +view. + + +No one doubts that our world at one time consisted of crystalline +rocks, and that it is to their disintegration through the action of +air, water, changes of temperature, rivers, waves of the sea, +earthquakes and volcanic outbursts, that we owe our sedimentary +formations. These after being consolidated and sometimes +recrystallized, have often been again disintegrated. Denudation +means the removal of such disintegrated matter to a lower level. +Of the many striking results due to the modern progress of geology +there are hardly any more striking than those which relate to +denudation. It was long ago seen that there must have been an +immense amount of denudation; but until the successive formations +were carefully mapped and measured, no one fully realised how great +was the amount. One of the first and most remarkable memoirs ever +published on this subject was that by Ramsay, {57} who in 1846 +showed that in Wales from 9000 to 11,000 feet in thickness of solid +rock had been stripped off large tracks of country. Perhaps the +plainest evidence of great denudation is afforded by faults or +cracks, which extend for many miles across certain districts, with +the strata on one side raised even ten thousand feet above the +corresponding strata on the opposite side; and yet there is not a +vestige of this gigantic displacement visible on the surface of the +land. A huge pile of rock has been planed away on one side and not +a remnant left. + +Until the last twenty or thirty years, most geologists thought that +the waves of the sea were the chief agents in the work of +denudation; but we may now feel sure that air and rain, aided by +streams and rivers, are much more powerful agents,--that is if we +consider the whole area of the land. The long lines of escarpment +which stretch across several parts of England were formerly +considered to be undoubtedly ancient coast-lines; but we now know +that they stand up above the general surface merely from resisting +air, rain and frost better than the adjoining formations. It has +rarely been the good fortune of a geologist to bring conviction to +the minds of his fellow-workers on a disputed point by a single +memoir; but Mr. Whitaker, of the Geological Survey of England, was +so fortunate when, in 1867, he published his paper "On sub-aerial +Denudation, and on Cliffs and Escarpments of the Chalk." {58} +Before this paper appeared, Mr. A. Tylor had adduced important +evidence on sub-aerial denudation, by showing that the amount of +matter brought down by rivers must infallibly lower the level of +their drainage basins by many feet in no immense lapse of time. +This line of argument has since been followed up in the most +interesting manner by Archibald Geikie, Croll and others, in a +series of valuable memoirs. {59} For the sake of those who have +never attended to this subject, a single instance may be here +given, namely, that of the Mississippi, which is chosen because the +amount of sediment brought down by this great river has been +investigated with especial care by order of the United States +Government. The result is, as Mr. Croll shows, that the mean level +of its enormous area of drainage must be lowered 1/4566 of a foot +annually, or 1 foot in 4566 years. Consequently, taking the best +estimate of the mean height of the North American continent, viz. +748 feet, and looking to the future, the whole of the great +Mississippi basin will be washed away, and "brought down to the +sea-level in less than 4,500,000 years, if no elevation of the land +takes place." Some rivers carry down much more sediment relatively +to their size, and some much less than the Mississippi. + +Disintegrated matter is carried away by the wind as well as by +running water. During volcanic outbursts much rock is triturated +and is thus widely dispersed; and in all arid countries the wind +plays an important part in the removal of such matter. Wind-driven +sand also wears down the hardest rocks. I have shown {60} that +during four months of the year a large quantity of dust is blown +from the north-western shores of Africa, and falls on the Atlantic +over a space of 1600 miles in latitude, and for a distance of from +300 to 600 miles from the coast. But dust has been seen to fall at +a distance of 1030 miles from the shores of Africa. During a stay +of three weeks at St. Jago in the Cape Verde Archipelago, the +atmosphere was almost always hazy, and extremely fine dust coming +from Africa was continually falling. In some of this dust which +fell in the open ocean at a distance of between 330 and 380 miles +from the African coast, there were many particles of stone, about +1/1000 of an inch square. Nearer to the coast the water has been +seen to be so much discoloured by the falling dust, that a sailing +vessel left a track behind her. In countries, like the Cape Verde +Archipelago, where it seldom rains and there are no frosts, the +solid rock nevertheless disintegrates; and in conformity with the +views lately advanced by a distinguished Belgian geologist, De +Koninck, such disintegration may be attributed in chief part to the +action of the carbonic and nitric acids, together with the nitrates +and nitrites of ammonia, dissolved in the dew. + +In all humid, even moderately humid, countries, worms aid in the +work of denudation in several ways. The vegetable mould which +covers, as with a mantle, the surface of the land, has all passed +many times through their bodies. Mould differs in appearance from +the subsoil only in its dark colour, and in the absence of +fragments or particles of stone (when such are present in the +subsoil), larger than those which can pass through the alimentary +canal of a worm. This sifting of the soil is aided, as has already +been remarked, by burrowing animals of many kinds, especially by +ants. In countries where the summer is long and dry, the mould in +protected places must be largely increased by dust blown from other +and more exposed places. For instance, the quantity of dust +sometimes blown over the plains of La Plata, where there are no +solid rocks, is so great, that during the "gran seco," 1827 to +1830, the appearance of the land, which is here unenclosed, was so +completely changed that the inhabitants could not recognise the +limits of their own estates, and endless lawsuits arose. Immense +quantities of dust are likewise blown about in Egypt and in the +south of France. In China, as Richthofen maintains, beds appearing +like fine sediment, several hundred feet in thickness and extending +over an enormous area, owe their origin to dust blown from the high +lands of central Asia. {61} In humid countries like Great Britain, +as long as the land remains in its natural state clothed with +vegetation, the mould in any one place can hardly be much increased +by dust; but in its present condition, the fields near high roads, +where there is much traffic, must receive a considerable amount of +dust, and when fields are harrowed during dry and windy weather, +clouds of dust may be seen to be blown away. But in all these +cases the surface-soil is merely transported from one place to +another. The dust which falls so thickly within our houses +consists largely of organic matter, and if spread over the land +would in time decay and disappear almost entirely. It appears, +however, from recent observations on the snow-fields of the Arctic +regions, that some little meteoric dust of extra mundane origin is +continually falling. + +The dark colour of ordinary mould is obviously due to the presence +of decaying organic matter, which, however, is present in but small +quantities. The loss of weight which mould suffers when heated to +redness seems to be in large part due to water in combination being +dispelled. In one sample of fertile mould the amount of organic +matter was ascertained to be only 1.76 per cent.; in some +artificially prepared soil it was as much as 5.5 per cent., and in +the famous black soil of Russia from 5 to even 12 per cent. {62} +In leaf-mould formed exclusively by the decay of leaves the amount +is much greater, and in peat the carbon alone sometimes amounts to +64 per cent.; but with these latter cases we are not here +concerned. The carbon in the soil tends gradually to oxidise and +to disappear, except where water accumulates and the climate is +cool; {63} so that in the oldest pasture-land there is no great +excess of organic matter, notwithstanding the continued decay of +the roots and the underground stems of plants, and the occasional +addition of manure. The disappearance of the organic matter from +mould is probably much aided by its being brought again and again +to the surface in the castings of worms. + +Worms, on the other hand, add largely to the organic matter in the +soil by the astonishing number of half-decayed leaves which they +draw into their burrows to a depth of 2 or 3 inches. They do this +chiefly for obtaining food, but partly for closing the mouths of +their burrows and for lining the upper part. The leaves which they +consume are moistened, torn into small shreds, partially digested, +and intimately commingled with earth; and it is this process which +gives to vegetable mould its uniform dark tint. It is known that +various kinds of acids are generated by the decay of vegetable +matter; and from the contents of the intestines of worms and from +their castings being acid, it seems probable that the process of +digestion induces an analogous chemical change in the swallowed, +triturated, and half-decayed leaves. The large quantity of +carbonate of lime secreted by the calciferous glands apparently +serves to neutralise the acids thus generated; for the digestive +fluid of worms will not act unless it be alkaline. As the contents +of the upper part of their intestines are acid, the acidity can +hardly be due to the presence of uric acid. We may therefore +conclude that the acids in the alimentary canal of worms are formed +during the digestive process; and that probably they are nearly of +the same nature as those in ordinary mould or humus. The latter +are well known to have the power of de-oxidising or dissolving per- +oxide of iron, as may be seen wherever peat overlies red sand, or +where a rotten root penetrates such sand. Now I kept some worms in +a pot filled with very fine reddish sand, consisting of minute +particles of silex coated with the red oxide of iron; and the +burrows, which the worms made through this sand, were lined or +coated in the usual manner with their castings, formed of the sand +mingled with their intestinal secretions and the refuse of the +digested leaves; and this sand had almost wholly lost its red +colour. When small portions of it were placed under the +microscope, most of the grains were seen to be transparent and +colourless, owing to the dissolution of the oxide; whilst almost +all the grains taken from other parts of the pot were coated with +the oxide. Acetic acid produced hardly any effect on his sand; and +even hydrochloric, nitric and sulphuric acids, diluted as in the +Pharmacopoeia, produced less effect than did the acids in the +intestines of the worms. + +Mr. A. A. Julien has lately collected all the extant information +about the acids generated in humus, which, according to some +chemists, amount to more than a dozen different kinds. These +acids, as well as their acid salts (i.e., in combination with +potash, soda, and ammonia), act energetically on carbonate of lime +and on the oxides of iron. It is also known that some of these +acids, which were called long ago by Thenard azohumic, are enabled +to dissolve colloid silica in proportion to the nitrogen which they +contain. {64} In the formation of these latter acids worms +probably afford some aid, for Dr. H. Johnson informs me that by +Nessler's test he found 0.018 per cent. of ammonia in their +castings. + +It may be here added that I have recently been informed by Dr. +Gilbert "that several square yards on his lawn were swept clean, +and after two or three weeks all the worm-castings on the space +were collected and dried. These were found to contain 0.35 of +nitrogen. This is from two to three times as much as we find in +our ordinary arable surface-soil; more than in our ordinary pasture +surface-soil; but less than in rich kitchen-garden mould. +Supposing a quantity of castings equal to 10 tons in the dry state +were annually deposited on an acre, this would represent a manuring +of 78 lbs. of nitrogen per acre per annum; and this is very much +more than the amount of nitrogen in the annual yield of hay per +acre, if raised without any nitrogenous manure. Obviously, so far +as the nitrogen in the castings is derived from surface-growth or +from surface-soil, it is not a gain to the latter; but so far as it +is derived from below, it is a gain." + +The several humus-acids, which appear, as we have just seen, to be +generated within the bodies of worms during the digestive process, +and their acid salts, play a highly important part, according to +the recent observations of Mr. Julien, in the disintegration of +various kinds of rocks. It has long been known that the carbonic +acid, and no doubt nitric and nitrous acids, which are present in +rain-water, act in like manner. There is, also, a great excess of +carbonic acid in all soils, especially in rich soils, and this is +dissolved by the water in the ground. The living roots of plants, +moreover, as Sachs and others have shown, quickly corrode and leave +their impressions on polished slabs of marble, dolomite and +phosphate of lime. They will attack even basalt and sandstone. +{65} But we are not here concerned with agencies which are wholly +independent of the action of worms. + +The combination of any acid with a base is much facilitated by +agitation, as fresh surfaces are thus continually brought into +contact. This will be thoroughly effected with the particles of +stone and earth in the intestines of worms, during the digestive +process; and it should be remembered that the entire mass of the +mould over every field, passes, in the course of a few years, +through their alimentary canals. Moreover as the old burrows +slowly collapse, and as fresh castings are continually brought to +the surface, the whole superficial layer of mould slowly revolves +or circulates; and the friction of the particles one with another +will rub off the finest films of disintegrated matter as soon as +they are formed. Through these several means, minute fragments of +rocks of many kinds and mere particles in the soil will be +continually exposed to chemical decomposition; and thus the amount +of soil will tend to increase. + +As worms line their burrows with their castings, and as the burrows +penetrate to a depth of 5 or 6, or even more feet, some small +amount of the humus-acids will be carried far down, and will there +act on the underlying rocks and fragments of rock. Thus the +thickness of the soil, if none be removed from the surface, will +steadily though slowly tend to increase; but the accumulation will +after a time delay the disintegration of the underlying rocks and +of the more deeply seated particles. For the humus-acids which are +generated chiefly in the upper layer of vegetable mould, are +extremely unstable compounds, and are liable to decomposition +before they reach any considerable depth. {66} A thick bed of +overlying soil will also check the downward extension of great +fluctuations of temperature, and in cold countries will check the +powerful action of frost. The free access of air will likewise be +excluded. From these several causes disintegration would be almost +arrested, if the overlying mould were to increase much in +thickness, owing to none or little being removed from the surface. +{67} In my own immediate neighbourhood we have a curious proof how +effectually a few feet of clay checks some change which goes on in +flints, lying freely exposed; for the large ones which have lain +for some time on the surface of ploughed fields cannot be used for +building; they will not cleave properly, and are said by the +workmen to be rotten. {68} It is therefore necessary to obtain +flints for building purposes from the bed of red clay overlying the +chalk (the residue of its dissolution by rain-water) or from the +chalk itself. + +Not only do worms aid directly in the chemical disintegration of +rocks, but there is good reason to believe that they likewise act +in a direct and mechanical manner on the smaller particles. All +the species which swallow earth are furnished with gizzards; and +these are lined with so thick a chitinous membrane, that Perrier +speaks of it, {69} as "une veritable armature." The gizzard is +surrounded by powerful transverse muscles, which, according to +Claparede, are about ten times as thick as the longitudinal ones; +and Perrier saw them contracting energetically. Worms belonging to +one genus, Digaster, have two distinct but quite similar gizzards; +and in another genus, Moniligaster, the second gizzard consists of +four pouches, one succeeding the other, so that it may almost be +said to have five gizzards. {70} In the same manner as +gallinaceous and struthious birds swallow stones to aid in the +trituration of their food, so it appears to be with terricolous +worms. The gizzards of thirty-eight of our common worms were +opened, and in twenty-five of them small stones or grains of sand, +sometimes together with the hard calcareous concretions formed +within the anterior calciferous glands, were found, and in two +others concretions alone. In the gizzards of the remaining worms +there were no stones; but some of these were not real exceptions, +as the gizzards were opened late in the autumn, when the worms had +ceased to feed and their gizzards were quite empty. {71} + +When worms make their burrows through earth abounding with little +stones, no doubt many will be unavoidably swallowed; but it must +not be supposed that this fact accounts for the frequency with +which stones and sand are found in their gizzards. For beads of +glass and fragments of brick and of hard tiles were scattered over +the surface of the earth, in pots in which worms were kept and had +already made their burrows; and very many of these beads and +fragments were picked up and swallowed by the worms, for they were +found in their castings, intestines, and gizzards. They even +swallowed the coarse red dust, formed by the pounding of the tiles. +Nor can it be supposed that they mistook the beads and fragments +for food; for we have seen that their taste is delicate enough to +distinguish between different kinds of leaves. It is therefore +manifest that they swallow hard objects, such as bits of stone, +beads of glass and angular fragments of bricks or tiles for some +special purpose; and it can hardly be doubted that this is to aid +their gizzards in crushing and grinding the earth, which they so +largely consume. That such hard objects are not necessary for +crushing leaves, may be inferred from the fact that certain +species, which live in mud or water and feed on dead or living +vegetable matter, but which do not swallow earth, are not provided +with gizzards, {72} and therefore cannot have the power of +utilising stones. + +During the grinding process, the particles of earth must be rubbed +against one another, and between the stones and the tough lining +membrane of the gizzard. The softer particles will thus suffer +some attrition, and will perhaps even be crushed. This conclusion +is supported by the appearance of freshly ejected castings, for +these often reminded me of the appearance of paint which has just +been ground by a workman between two flat stones. Morren remarks +that the intestinal canal is "impleta tenuissima terra, veluti in +pulverem redacta." {73} Perrier also speaks of "l'etat de pate +excessivement fine a laquelle est reduite la terre qu'ils +rejettent," &c. {74} + +As the amount of trituration which the particles of earth undergo +in the gizzards of worms possesses some interest (as we shall +hereafter see), I endeavoured to obtain evidence on this head by +carefully examining many of the fragments which had passed through +their alimentary canals. With worms living in a state of nature, +it is of course impossible to know how much the fragments may have +been worn before they were swallowed. It is, however, clear that +worms do not habitually select already rounded particles, for +sharply angular bits of flint and of other hard rocks were often +found in their gizzards or intestines. On three occasions sharp +spines from the stems of rose-bushes were thus found. Worms kept +in confinement repeatedly swallowed angular fragments of hard tile, +coal, cinders, and even the sharpest fragments of glass. +Gallinaceous and struthious birds retain the same stones in their +gizzards for a long time, which thus become well rounded; but this +does not appear to be the case with worms, judging from the large +number of the fragments of tiles, glass beads, stones, &c., +commonly found in their castings and intestines. So that unless +the same fragments were to pass repeatedly through their gizzards, +visible signs of attrition in the fragments could hardly be +expected, except perhaps in the case of very soft stones. + +I will now give such evidence of attrition as I have been able to +collect. In the gizzards of some worms dug out of a thin bed of +mould over the chalk, there were many well-rounded small fragments +of chalk, and two fragments of the shells of a land-mollusc (as +ascertained by their microscopical structure), which latter were +not only rounded but somewhat polished. The calcareous concretions +formed in the calciferous glands, which are often found in their +gizzards, intestines, and occasionally in their castings, when of +large size, sometimes appeared to have been rounded; but with all +calcareous bodies the rounded appearance may be partly or wholly +due to their corrosion by carbonic acid and the humus-acids. In +the gizzards of several worms collected in my kitchen garden near a +hothouse, eight little fragments of cinders were found, and of +these, six appeared more or less rounded, as were two bits of +brick; but some other bits were not at all rounded. A farm-road +near Abinger Hall had been covered seven years before with brick- +rubbish to the depth of about 6 inches; turf had grown over this +rubbish on both sides of the road for a width of 18 inches, and on +this turf there were innumerable castings. Some of them were +coloured of a uniform red owing to the presence of much brick-dust, +and they contained many particles of brick and of hard mortar from +1 to 3 mm. in diameter, most of which were plainly rounded; but all +these particles may have been rounded before they were protected by +the turf and were swallowed, like those on the bare parts of the +road which were much worn. A hole in a pasture-field had been +filled up with brick-rubbish at the same time, viz., seven years +ago, and was now covered with turf; and here the castings contained +very many particles of brick, all more or less rounded; and this +brick-rubbish, after being shot into the hole, could not have +undergone any attrition. Again, old bricks very little broken, +together with fragments of mortar, were laid down to form walks, +and were then covered with from 4 to 6 inches of gravel; six little +fragments of brick were extracted from castings collected on these +walks, three of which were plainly worn. There were also very many +particles of hard mortar, about half of which were well rounded; +and it is not credible that these could have suffered so much +corrosion from the action of carbonic acid in the course of only +seven years. + +Much better evidence of the attrition of hard objects in the +gizzards of worms, is afforded by the state of the small fragments +of tiles or bricks, and of concrete in the castings thrown up where +ancient buildings once stood. As all the mould covering a field +passes every few years through the bodies of worms, the same small +fragments will probably be swallowed and brought to the surface +many times in the course of centuries. It should be premised that +in the several following cases, the finer matter was first washed +away from the castings, and then all the particles of bricks, tiles +and concrete were collected without any selection, and were +afterwards examined. Now in the castings ejected between the +tesserae on one of the buried floors of the Roman villa at Abinger, +there were many particles (from to 2 mm. in diameter) of tiles and +concrete, which it was impossible to look at with the naked eye or +through a strong lens, and doubt for a moment that they had almost +all undergone much attrition. I speak thus after having examined +small water-worn pebbles, formed from Roman bricks, which M. Henri +de Saussure had the kindness to send me, and which he had extracted +from sand and gravel beds, deposited on the shores of the Lake of +Geneva, at a former period when the water stood at about two metres +above its present level. The smallest of these water-worn pebbles +of brick from Geneva resembled closely many of those extracted from +the gizzards of worms, but the larger ones were somewhat smoother. + +Four castings found on the recently uncovered, tesselated floor of +the great room in the Roman villa at Brading, contained many +particles of tile or brick, of mortar, and of hard white cement; +and the majority of these appeared plainly worn. The particles of +mortar, however, seemed to have suffered more corrosion than +attrition, for grains of silex often projected from their surfaces. +Castings from within the nave of Beaulieu Abbey, which was +destroyed by Henry VIII., were collected from a level expanse of +turf, overlying the buried tesselated pavement, through which worm- +burrows passed; and these castings contained innumerable particles +of tiles and bricks, of concrete and cement, the majority of which +had manifestly undergone some or much attrition. There were also +many minute flakes of a micaceous slate, the points of which were +rounded. If the above supposition, that in all these cases the +same minute fragments have passed several times through the +gizzards of worms, be rejected, notwithstanding its inherent +probability, we must then assume that in all the above cases the +many rounded fragments found in the castings had all accidentally +undergone much attrition before they were swallowed; and this is +highly improbable. + +On the other hand it must be stated that fragments of ornamental +tiles, somewhat harder than common tiles or bricks, which had been +swallowed only once by worms kept in confinement, were with the +doubtful exception of one or two of the smallest grains, not at all +rounded. Nevertheless some of them appeared a little worn, though +not rounded. Notwithstanding these cases, if we consider the +evidence above given, there can be little doubt that the fragments, +which serve as millstones in the gizzards of worms, suffer, when of +a not very hard texture, some amount of attrition; and that the +smaller particles in the earth, which is habitually swallowed in +such astonishingly large quantities by worms, are ground together +and are thus levigated. If this be the case, the "terra +tenuissima,"--the "pate excessivement fine,"--of which the castings +largely consist, is in part due to the mechanical action of the +gizzard; {75} and this fine matter, as we shall see in the next +chapter, is that which is chiefly washed away from the innumerable +castings on every field during each heavy shower of rain. If the +softer stones yield at all, the harder ones will suffer some slight +amount of wear and tear. + +The trituration of small particles of stone in the gizzards of +worms is of more importance under a geological point of view than +may at first appear to be the case; for Mr. Sorby has clearly shown +that the ordinary means of disintegration, namely, running water +and the waves of the sea, act with less and less power on fragments +of rock the smaller they are. "Hence," as he remarks, "even making +no allowance for the extra buoying up of very minute particles by a +current of water, depending on surface cohesion, the effects of +wearing on the form of the grains must vary directly as their +diameter or thereabouts. If so, a grain of 1/10 an inch in +diameter would be worn ten times as much as one of an inch in +diameter, and at least a hundred times as much as one of 1/100 an +inch in diameter. Perhaps, then, we may conclude that a grain 1/10 +of an inch in diameter would be worn as much or more in drifting a +mile as a grain 1/1000 of an inch in being drifted 100 miles. On +the same principle a pebble one inch in diameter would be worn +relatively more by being drifted only a few hundred yards." {76} +Nor should we forget, in considering the power which worms exert in +triturating particles of rock, that there is good evidence that on +each acre of land, which is sufficiently damp and not too sandy, +gravelly or rocky for worms to inhabit, a weight of more than ten +tons of earth annually passes through their bodies and is brought +to the surface. The result for a country of the size of Great +Britain, within a period not very long in a geological sense, such +as a million years, cannot be insignificant; for the ten tons of +earth has to be multiplied first by the above number of years, and +then by the number of acres fully stocked with worms; and in +England, together with Scotland, the land which is cultivated and +is well fitted for these animals, has been estimated at above 32 +million acres. The product is 320 million million tons of earth. + + + +CHAPTER VI--THE DENUDATION OF THE LAND--continued. + + + +Denudation aided by recently ejected castings flowing down inclined +grass-covered surfaces--The amount of earth which annually flows +downwards--The effect of tropical rain on worm castings--The finest +particles of earth washed completely away from castings--The +disintegration of dried castings into pellets, and their rolling +down inclined surfaces--The formation of little ledges on hill- +sides, in part due to the accumulation of disintegrated castings-- +Castings blown to leeward over level land--An attempt to estimate +the amount thus blown--The degradation of ancient encampments and +tumuli--The preservation of the crowns and furrows on land +anciently ploughed--The formation and amount of mould over the +Chalk formation. + +We are now prepared to consider the more direct part which worms +take in the denudation of the land. When reflecting on sub-aerial +denudation, it formerly appeared to me, as it has to others, that a +nearly level or very gently inclined surface, covered with turf, +could suffer no loss during even a long lapse of time. It may, +however, be urged that at long intervals, debacles of rain or +water-spouts would remove all the mould from a very gentle slope; +but when examining the steep, turf-covered slopes in Glen Roy, I +was struck with the fact how rarely any such event could have +happened since the Glacial period, as was plain from the well- +preserved state of the three successive "roads" or lake-margins. +But the difficulty in believing that earth in any appreciable +quantity can be removed from a gently inclined surface, covered +with vegetation and matted with roots, is removed through the +agency of worms. For the many castings which are thrown up during +rain, and those thrown up some little time before heavy rain, flow +for a short distance down an inclined surface. Moreover much of +the finest levigated earth is washed completely away from the +castings. During dry weather castings often disintegrate into +small rounded pellets, and these from their weight often roll down +any slope. This is more especially apt to occur when they are +started by the wind, and probably when started by the touch of an +animal, however small. We shall also see that a strong wind blows +all the castings, even on a level field, to leeward, whilst they +are soft; and in like manner the pellets when they are dry. If the +wind blows in nearly the direction of an inclined surface, the +flowing down of the castings is much aided. + +The observations on which these several statements are founded must +now be given in some detail. Castings when first ejected are +viscid and soft; during rain, at which time worms apparently prefer +to eject them, they are still softer; so that I have sometimes +thought that worms must swallow much water at such times. However +this may be, rain, even when not very heavy, if long continued, +renders recently-ejected castings semi-fluid; and on level ground +they then spread out into thin, circular, flat discs, exactly as +would so much honey or very soft mortar, with all traces of their +vermiform structure lost. This latter fact was sometimes made +evident, when a worm had subsequently bored through a flat circular +disc of this kind, and heaped up a fresh vermiform mass in the +centre. These flat subsided discs have been repeatedly seen by me +after heavy rain, in many places on land of all kinds. + +On the flowing of wet castings, and the rolling of dry +disintegrated castings down inclined surfaces.--When castings are +ejected on an inclined surface during or shortly before heavy rain, +they cannot fail to flow a little down the slope. Thus, on some +steep slopes in Knole Park, which were covered with coarse grass +and had apparently existed in this state from time immemorial, I +found (Oct. 22, 1872) after several wet days that almost all the +many castings were considerably elongated in the line of the slope; +and that they now consisted of smooth, only slightly conical +masses. Whenever the mouths of the burrows could be found from +which the earth had been ejected, there was more earth below than +above them. After some heavy storms of rain (Jan. 25, 1872) two +rather steeply inclined fields near Down, which had formerly been +ploughed and were now rather sparsely clothed with poor grass, were +visited, and many castings extended down the slopes for a length of +5 inches, which was twice or thrice the usual diameter of the +castings thrown up on the level parts of these same fields. On +some fine grassy slopes in Holwood Park, inclined at angles between +8 degrees and 11 degrees 30 seconds with the horizon, where the +surface apparently had never been disturbed by the hand of man, +castings abounded in extraordinary numbers: and a space 16 inches +in length transversely to the slope and 6 inches in the line of the +slope, was completely coated, between the blades of grass, with a +uniform sheet of confluent and subsided castings. Here also in +many places the castings had flowed down the slope, and now formed +smooth narrow patches of earth, 6, 7, and 7.5 inches in length. +Some of these consisted of two castings, one above the other, which +had become so completely confluent that they could hardly be +distinguished. On my lawn, clothed with very fine grass, most of +the castings are black, but some are yellowish from earth having +been brought up from a greater depth than usual, and the flowing- +down of these yellow castings after heavy rain, could be clearly +seen where the slope was 5 degrees; and where it was less than 1 +degree some evidence of their flowing down could still be detected. +On another occasion, after rain which was never heavy, but which +lasted for 18 hours, all the castings on this same gently inclined +lawn had lost their vermiform structure; and they had flowed, so +that fully two-thirds of the ejected earth lay below the mouths of +the burrows. + +These observations led me to make others with more care. Eight +castings were found on my lawn, where the grass-blades are fine and +close together, and three others on a field with coarse grass. The +inclination of the surface at the eleven places where these +castings were collected varied between 4 degrees 30 seconds and 17 +degrees 30 seconds; the mean of the eleven inclinations being 9 +degrees 26 seconds. The length of the castings in the direction of +the slope was first measured with as much accuracy as their +irregularities would permit. It was found possible to make these +measurements within about of an inch, but one of the castings was +too irregular to admit of measurement. The average length in the +direction of the slope of the remaining ten castings was 2.03 +inches. The castings were then divided with a knife into two parts +along a horizontal line passing through the mouth of the burrow, +which was discovered by slicing off the turf; and all the ejected +earth was separately collected, namely, the part above the hole and +the part below. Afterwards these two parts were weighed. In every +case there was much more earth below than above; the mean weight of +that above being 103 grains, and of that below 205 grains; so that +the latter was very nearly double the former. As on level ground +castings are commonly thrown up almost equally round the mouths of +the burrows, this difference in weight indicates the amount of +ejected earth which had flowed down the slope. But very many more +observations would be requisite to arrive at any general result; +for the nature of the vegetation and other accidental +circumstances, such as the heaviness of the rain, the direction and +force of the wind, &c., appear to be more important in determining +the quantity of the earth which flows down a slope than its angle. +Thus with four castings on my lawn (included in the above eleven) +where the mean slope was 7 degrees 19 seconds, the difference in +the amount of earth above and below the burrows was greater than +with three other castings on the same lawn where the mean slope was +12 degrees 5 seconds. + +We may, however, take the above eleven cases, which are accurate as +far as they go, and calculate the weight of the ejected earth which +annually flows down a slope having a mean inclination of 9 degrees +26 seconds. This was done by my son George. It has been shown +that almost exactly two-thirds of the ejected earth is found below +the mouth of the burrow and one-third above it. Now if the two- +thirds which is below the hole be divided into two equal parts, the +upper half of this two-thirds exactly counterbalances the one-third +which is above the hole, so that as far as regards the one-third +above and the upper half of the two-thirds below, there is no flow +of earth down the hill-side. The earth constituting the lower half +of the two-thirds is, however, displaced through distances which +are different for every part of it, but which may be represented by +the distance between the middle point of the lower half of the two- +thirds and the hole. So that the average distance of displacement +is a half of the whole length of the worm-casting. Now the average +length of ten out of the above eleven castings was 2.03 inches, and +half of this we may take as being 1 inch. It may therefore be +concluded that one-third of the whole earth brought to the surface +was in these cases carried down the slope through 1 inch. {77} + +It was shown in the third chapter that on Leith Hill Common, dry +earth weighing at least 7.453 lbs. was brought up by worms to the +surface on a square yard in the course of a year. If a square yard +be drawn on a hillside with two of its sides horizontal, then it is +clear that only 1/36 part of the earth brought up on that square +yard would be near enough to its lower side to cross it, supposing +the displacement of the earth to be through one inch. But it +appears that only of the earth brought up can be considered to flow +downwards; hence 1/3 of 1/36 or 1/108 of 7.453 lbs. will cross the +lower side of our square yard in a year. Now 1/108 of 7.453 lbs. +is 1.1 oz. Therefore 1.1 oz. of dry earth will annually cross each +linear yard running horizontally along a slope having the above +inclination; or very nearly 7 lbs. will annually cross a horizontal +line, 100 yards in length, on a hill-side having this inclination. + +A more accurate, though still very rough, calculation can be made +of the bulk of earth, which in its natural damp state annually +flows down the same slope over a yard-line drawn horizontally +across it. From the several cases given in the third chapter, it +is known that the castings annually brought to the surface on a +square yard, if uniformly spread out would form a layer 0.2 of an +inch in thickness: it therefore follows by a calculation similar +to the one already given, that 1/3 of 0.2x36, or 2.4 cubic inches +of damp earth will annually cross a horizontal line one yard in +length on a hillside with the above inclination. This bulk of damp +castings was found to weigh 1.85 oz. Therefore 11.56 lbs. of damp +earth, instead of 7 lbs. of dry earth as by the former calculation, +would annually cross a line 100 yards in length on our inclined +surface. + +In these calculations it has been assumed that the castings flow a +short distance downwards during the whole year, but this occurs +only with those ejected during or shortly before rain; so that the +above results are thus far exaggerated. On the other hand, during +rain much of the finest earth is washed to a considerable distance +from the castings, even where the slope is an extremely gentle one, +and is thus wholly lost as far as the above calculations are +concerned. Castings ejected during dry weather and which have set +hard, lose in the same manner a considerable quantity of fine +earth. Dried castings, moreover, are apt to disintegrate into +little pellets, which often roll or are blown down any inclined +surface. Therefore the above result, namely, that 24 cubic inches +of earth (weighing 1.85 oz. whilst damp) annually crosses a yard- +line of the specified kind, is probably not much if at all +exaggerated. + +This amount is small; but we should bear in mind how many branching +valleys intersect most countries, the whole length of which must be +very great; and that earth is steadily travelling down both turf- +covered sides of each valley. For every 100 yards in length in a +valley with sides sloping as in the foregoing cases, 480 cubic +inches of damp earth, weighing above 23 pounds, will annually reach +the bottom. Here a thick bed of alluvium will accumulate, ready to +be washed away in the course of centuries, as the stream in the +middle meanders from side to side. + +If it could be shown that worms generally excavate their burrows at +right angles to an inclined surface, and this would be their +shortest course for bringing up earth from beneath, then as the old +burrows collapsed from the weight of the superincumbent soil, the +collapsing would inevitably cause the whole bed of vegetable mould +to sink or slide slowly down the inclined surface. But to +ascertain the direction of many burrows was found too difficult and +troublesome. A straight piece of wire was, however, pushed into +twenty-five burrows on several sloping fields, and in eight cases +the burrows were nearly at right angles to the slope; whilst in the +remaining cases they were indifferently directed at various angles, +either upwards or downwards with respect to the slope. + +In countries where the rain is very heavy, as in the tropics, the +castings appear, as might have been expected, to be washed down in +a greater degree than in England. Mr. Scott informs me that near +Calcutta the tall columnar castings (previously described), the +diameter of which is usually between 1 and 1.5 inch, subside on a +level surface, after heavy rain, into almost circular, thin, flat +discs, between 3 and 4 and sometimes 5 inches in diameter. Three +fresh castings, which had been ejected in the Botanic Gardens "on a +slightly inclined, grass-covered, artificial bank of loamy clay," +were carefully measured, and had a mean height of 2.17, and a mean +diameter of 1.43 inches; these after heavy rain, formed elongated +patches of earth, with a mean length in the direction of the slope +of 5.83 inches. As the earth had spread very little up the slope, +a large part, judging from the original diameter of these castings, +must have flowed bodily downwards about 4 inches. Moreover some of +the finest earth of which they were composed must have been washed +completely away to a still greater distance. In drier sites near +Calcutta, a species of worm ejects its castings, not in vermiform +masses, but in little pellets of varying sizes: these are very +numerous in some places, and Mr. Scott says that they "are washed +away by every shower." + +I was led to believe that a considerable quantity of fine earth is +washed quite away from castings during rain, from the surfaces of +old ones being often studded with coarse particles. Accordingly a +little fine precipitated chalk, moistened with saliva or gum-water, +so as to be slightly viscid and of the same consistence as a fresh +casting, was placed on the summits of several castings and gently +mixed with them. These castings were then watered through a very +fine rose, the drops from which were closer together than those of +rain, but not nearly so large as those in a thunderstorm; nor did +they strike the ground with nearly so much force as drops during +heavy rain. A casting thus treated subsided with surprising +slowness, owing as I suppose to its viscidity. It did not flow +bodily down the grass-covered surface of the lawn, which was here +inclined at an angle of 16 degrees 20 seconds; nevertheless many +particles of the chalk were found three inches below the casting. +The experiment was repeated on three other castings on different +parts of the lawn, which sloped at 2 degrees 30 seconds, 3 degrees +and 6 degrees; and particles of chalk could be seen between 4 and 5 +inches below the casting; and after the surface had become dry, +particles were found in two cases at a distance of 5 and 6 inches. +Several other castings with precipitated chalk placed on their +summits were left to the natural action of the rain. In one case, +after rain which was not heavy, the casting was longitudinally +streaked with white. In two other cases the surface of the ground +was rendered somewhat white for a distance of one inch from the +casting; and some soil collected at a distance of 2.5 inches, where +the slope was 7 degrees, effervesced slightly when placed in acid. +After one or two weeks, the chalk was wholly or almost wholly +washed away from all the castings on which it had been placed, and +these had recovered their natural colour. + +It may be here remarked that after very heavy rain shallow pools +may be seen on level or nearly level fields, where the soil is not +very porous, and the water in them is often slightly muddy; when +such little pools have dried, the leaves and blades of grass at +their bottoms are generally coated with a thin layer of mud. This +mud I believe is derived in large part from recently ejected +castings. + +Dr. King informs me that the majority of the before described +gigantic castings, which he found on a fully exposed, bare, +gravelly knoll on the Nilgiri Mountains in India, had been more or +less weathered by the previous north-east monsoon; and most of them +presented a subsided appearance. The worms here eject their +castings only during the rainy season; and at the time of Dr. +King's visit no rain had fallen for 110 days. He carefully +examined the ground between the place where these huge castings +lay, and a little watercourse at the base of the knoll, and nowhere +was there any accumulation of fine earth, such as would necessarily +have been left by the disintegration of the castings if they had +not been wholly removed. He therefore has no hesitation in +asserting that the whole of these huge castings are annually washed +during the two monsoons (when about 100 inches of rain fall) into +the little water-course, and thence into the plains lying below at +a depth of 3000 or 4000 feet. + +Castings ejected before or during dry weather become hard, +sometimes surprisingly hard, from the particles of earth having +been cemented together by the intestinal secretions. Frost seems +to be less effective in their disintegration than might have been +expected. Nevertheless they readily disintegrate into small +pellets, after being alternately moistened with rain and again +dried. Those which have flowed during rain down a slope, +disintegrate in the same manner. Such pellets often roll a little +down any sloping surface; their descent being sometimes much aided +by the wind. The whole bottom of a broad dry ditch in my grounds, +where there were very few fresh castings, was completely covered +with these pellets or disintegrated castings, which had rolled down +the steep sides, inclined at an angle of 27 degrees. + +Near Nice, in places where the great cylindrical castings, +previously described, abound, the soil consists of very fine +arenaceo-calcareous loam; and Dr. King informs me that these +castings are extremely liable to crumble during dry weather into +small fragments, which are soon acted on by rain, and then sink +down so as to be no longer distinguishable from the surrounding +soil. He sent me a mass of such disintegrated castings, collected +on the top of a bank, where none could have rolled down from above. +They must have been ejected within the previous five or six months, +but they now consisted of more or less rounded fragments of all +sizes, from 0.75 of an inch in diameter to minute grains and mere +dust. Dr. King witnessed the crumbling process whilst drying some +perfect castings, which he afterwards sent me. Mr. Scott also +remarks on the crumbling of the castings near Calcutta and on the +mountains of Sikkim during the hot and dry season. + +When the castings near Nice had been ejected on an inclined +surface, the disintegrated fragments rolled downwards, without +losing their distinctive shape; and in some places could "be +collected in basketfuls." Dr. King observed a striking instance of +this fact on the Corniche road, where a drain, about 2.5 feet wide +and 9 inches deep, had been made to catch the surface drainage from +the adjoining hill-side. The bottom of this drain was covered for +a distance of several hundred yards, to a depth of from 1.5 to 3 +inches, by a layer of broken castings, still retaining their +characteristic shape. Nearly all these innumerable fragments had +rolled down from above, for extremely few castings had been ejected +in the drain itself. The hill-side was steep, but varied much in +inclination, which Dr. King estimated at from 30 degrees to 60 +degrees with the horizon. He climbed up the slope, and "found +every here and there little embankments, formed by fragments of the +castings that had been arrested in their downward progress by +irregularities of the surface, by stones, twigs, &c. One little +group of plants of Anemone hortensis had acted in this manner, and +quite a small bank of soil had collected round it. Much of this +soil had crumbled down, but a great deal of it still retained the +form of castings." Dr. King dug up this plant, and was struck with +the thickness of the soil which must have recently accumulated over +the crown of the rhizoma, as shown by the length of the bleached +petioles, in comparison with those of other plants of the same +kind, where there had been no such accumulation. The earth thus +accumulated had no doubt been secured (as I have everywhere seen) +by the smaller roots of the plants. After describing this and +other analogous cases, Dr. King concludes: "I can have no doubt +that worms help greatly in the process of denudation." + +Ledges of earth on steep hill-sides.--Little horizontal ledges, one +above another, have been observed on steep grassy slopes in many +parts of the world. The formation has been attributed to animals +travelling repeatedly along the slope in the same horizontal lines +while grazing, and that they do thus move and use the ledges is +certain; but Professor Henslow (a most careful observer) told Sir +J. Hooker that he was convinced that this was not the sole cause of +their formation. Sir J. Hooker saw such ledges on the Himalayan +and Atlas ranges, where there were no domesticated animals and not +many wild ones; but these latter would, it is probable, use the +ledges at night while grazing like our domesticated animals. A +friend observed for me the ledges on the Alps of Switzerland, and +states that they ran at 3 or 4 ft. one above the other, and were +about a foot in breadth. They had been deeply pitted by the feet +of grazing cows. Similar ledges were observed by the same friend +on our Chalk downs, and on an old talus of chalk-fragments (thrown +out of a quarry) which had become clothed with turf. + +My son Francis examined a Chalk escarpment near Lewes; and here on +a part which was very steep, sloping at 40 degrees with the +horizon, about 30 flat ledges extended horizontally for more than +100 yards, at an average distance of about 20 inches, one beneath +the other. They were from 9 to 10 inches in breadth. When viewed +from a distance they presented a striking appearance, owing to +their parallelism; but when examined closely, they were seen to be +somewhat sinuous, and one often ran into another, giving the +appearance of the ledge having forked into two. They are formed of +light-coloured earth, which on the outside, where thickest, was in +one case 9 inches, and in another case between 6 and 7 inches in +thickness. Above the ledges, the thickness of the earth over the +chalk was in the former case 4 and in the latter only 3 inches. +The grass grew more vigorously on the outer edges of the ledges +than on any other part of the slope, and here formed a tufted +fringe. Their middle part was bare, but whether this had been +caused by the trampling of sheep, which sometimes frequent the +ledges, my son could not ascertain. Nor could he feel sure how +much of the earth on the middle and bare parts, consisted of +disintegrated worm-castings which had rolled down from above; but +he felt convinced that some had thus originated; and it was +manifest that the ledges with their grass-fringed edges would +arrest any small object rolling down from above. + +At one end or side of the bank bearing these ledges, the surface +consisted in parts of bare chalk, and here the ledges were very +irregular. At the other end of the bank, the slope suddenly became +less steep, and here the ledges ceased rather abruptly; but little +embankments only a foot or two in length were still present. The +slope became steeper lower down the hill, and the regular ledges +then reappeared. Another of my sons observed, on the inland side +of Beachy Head, where the surface sloped at about 25 degrees, many +short little embankments like those just mentioned. They extended +horizontally and were from a few inches to two or three feet in +length. They supported tufts of grass growing vigorously. The +average thickness of the mould of which they were formed, taken +from nine measurements, was 4.5 inches; while that of the mould +above and beneath them was on an average only 3.2 inches, and on +each side, on the same level, 3.1 inches. On the upper parts of +the slope, these embankments showed no signs of having been +trampled on by sheep, but in the lower parts such signs were fairly +plain. No long continuous ledges had here been formed. + +If the little embankments above the Corniche road, which Dr. King +saw in the act of formation by the accumulation of disintegrated +and rolled worm-castings, were to become confluent along horizontal +lines, ledges would be formed. Each embankment would tend to +extend laterally by the lateral extension of the arrested castings; +and animals grazing on a steep slope would almost certainly make +use of every prominence at nearly the same level, and would indent +the turf between them; and such intermediate indentations would +again arrest the castings. An irregular ledge when once formed +would also tend to become more regular and horizontal by some of +the castings rolling laterally from the higher to the lower parts, +which would thus be raised. Any projection beneath a ledge would +not afterwards receive disintegrated matter from above, and would +tend to be obliterated by rain and other atmospheric agencies. +There is some analogy between the formation, as here supposed, of +these ledges, and that of the ripples of wind-drifted sand as +described by Lyell. {78} + +The steep, grass-covered sides of a mountainous valley in +Westmoreland, called Grisedale, was marked in many places with +innumerable lines of miniature cliffs, with almost horizontal, +little ledges at their bases. Their formation was in no way +connected with the action of worms, for castings could not anywhere +be seen (and their absence is an inexplicable fact), although the +turf lay in many places over a considerable thickness of boulder- +clay and moraine rubbish. Nor, as far as I could judge, was the +formation of these little cliffs at all closely connected with the +trampling of cows or sheep. It appeared as if the whole +superficial, somewhat argillaceous earth, while partially held +together by the roots of the grasses, had slided a little way down +the mountain sides; and in thus sliding, had yielded and cracked in +horizontal lines, transversely to the slope. + +Castings blown to leeward by the wind.--We have seen that moist +castings flow, and that disintegrated castings roll down any +inclined surface; and we shall now see that castings, recently +ejected on level grass-covered surfaces, are blown during gales of +wind accompanied by rain to leeward. This has been observed by me +many times on many fields during several successive years. After +such gales, the castings present a gently inclined and smooth, or +sometimes furrowed, surface to windward, while they are steeply +inclined or precipitous to leeward, so that they resemble on a +miniature scale glacier-ground hillocks of rock. They are often +cavernous on the leeward side, from the upper part having curled +over the lower part. During one unusually heavy south-west gale +with torrents of rain, many castings were wholly blown to leeward, +so that the mouths of the burrows were left naked and exposed on +the windward side. Recent castings naturally flow down an inclined +surface, but on a grassy field, which sloped between 10 degrees and +15 degrees, several were found after a heavy gale blown up the +slope. This likewise occurred on another occasion on a part of my +lawn where the slope was somewhat less. On a third occasion, the +castings on the steep, grass-covered sides of a valley, down which +a gale had blown, were directed obliquely instead of straight down +the slope; and this was obviously due to the combined action of the +wind and gravity. Four castings on my lawn, where the downward +inclination was 0 degrees 45 seconds, 1 degree, 3 degrees and 3 +degrees 30 seconds (mean 2 degrees 45 seconds) towards the north- +east, after a heavy south-west gale with rain, were divided across +the mouths of the burrows and weighed in the manner formerly +described. The mean weight of the earth below the mouths of +burrows and to leeward, was to that above the mouths and on the +windward side as 2.75 to 1; whereas we have seen that with several +castings which had flowed down slopes having a mean inclination of +9 degrees 26 seconds, and with three castings where the inclination +was above 12 degrees; the proportional weight of the earth below to +that above the burrows was as only 2 to 1. These several cases +show how efficiently gales of wind accompanied by rain act in +displacing recently ejected castings. We may therefore conclude +that even a moderately strong wind will produce some slight effect +on them. + +Dry and indurated castings, after their disintegration into small +fragments or pellets, are sometimes, probably often, blown by a +strong wind to leeward. This was observed on four occasions, but I +did not sufficiently attend to this point. One old casting on a +gently sloping bank was blown quite away by a strong south-west +wind. Dr. King believes that the wind removes the greater part of +the old crumbling castings near Nice. Several old castings on my +lawn were marked with pins and protected from any disturbance. +They were examined after an interval of 10 weeks, during which time +the weather had been alternately dry and rainy. Some, which were +of a yellowish colour had been washed almost completely away, as +could be seen by the colour of the surrounding ground. Others had +completely disappeared, and these no doubt had been blown away. +Lastly, others still remained and would long remain, as blades of +grass had grown through them. On poor pasture-land, which has +never been rolled and has not been much trampled on by animals, the +whole surface is sometimes dotted with little pimples, through and +on which grass grows; and these pimples consist of old worm- +castings. + +In all the many observed cases of soft castings blown to leeward, +this had been effected by strong winds accompanied by rain. As +such winds in England generally blow from the south and south-west, +earth must on the whole tend to travel over our fields in a north +and north-east direction. This fact is interesting, because it +might be thought that none could be removed from a level, grass- +covered surface by any means. In thick and level woods, protected +from the wind, castings will never be removed as long as the wood +lasts; and mould will here tend to accumulate to the depth at which +worms can work. I tried to procure evidence as to how much mould +is blown, whilst in the state of castings, by our wet southern +gales to the north-east, over open and flat land, by looking to the +level of the surface on opposite sides of old trees and hedge-rows; +but I failed owing to the unequal growth of the roots of trees and +to most pasture-land having been formerly ploughed. + +On an open plain near Stonehenge, there exist shallow circular +trenches, with a low embankment outside, surrounding level spaces +50 yards in diameter. These rings appear very ancient, and are +believed to be contemporaneous with the Druidical stones. Castings +ejected within these circular spaces, if blown to the north-east by +south-west winds would form a layer of mould within the trench, +thicker on the north-eastern than on any other side. But the site +was not favourable for the action of worms, for the mould over the +surrounding Chalk formation with flints, was only 3.37 inches in +thickness, from a mean of six observations made at a distance of 10 +yards outside the embankment. The thickness of the mould within +two of the circular trenches was measured every 5 yards all round, +on the inner sides near the bottom. My son Horace protracted these +measurements on paper; and though the curved line representing the +thickness of the mould was extremely irregular, yet in both +diagrams it could be seen to be thicker on the north-eastern side +than elsewhere. When a mean of all the measurements in both the +trenches was laid down and the line smoothed, it was obvious that +the mould was thickest in the quarter of the circle between north- +west and north-east; and thinnest in the quarter between south-east +and south-west, especially at this latter point. Besides the +foregoing measurements, six others were taken near together in one +of the circular trenches, on the north-east side; and the mould +here had a mean thickness of 2.29 inches; while the mean of six +other measurements on the south-west side was only 1.46 inches. +These observations indicate that the castings had been blown by the +south-west winds from the circular enclosed space into the trench +on the north-east side; but many more measurements in other +analogous cases would be requisite for a trustworthy result. + +The amount of fine earth brought to the surface under the form of +castings, and afterwards transported by the winds accompanied by +rain, or that which flows and rolls down an inclined surface, no +doubt is small in the course of a few scores of years; for +otherwise all the inequalities in our pasture fields would be +smoothed within a much shorter period than appears to be the case. +But the amount which is thus transported in the course of thousands +of years cannot fail to be considerable and deserves attention. E. +de Beaumont looks at the vegetable mould which everywhere covers +the land as a fixed line, from which the amount of denudation may +be measured. {79} He ignores the continued formation of fresh +mould by the disintegration of the underlying rocks and fragments +of rock; and it is curious to find how much more philosophical were +the views maintained long ago, by Playfair, who, in 1802, wrote, +"In the permanence of a coat of vegetable mould on the surface of +the earth, we have a demonstrative proof of the continued +destruction of the rocks." {80} + +Ancient encampments and tumuli.--E. de Beaumont adduces the present +state of many ancient encampments and tumuli and of old ploughed +fields, as evidence that the surface of the land undergoes hardly +any degradation. But it does not appear that he ever examined the +thickness of the mould over different parts of such old remains. +He relies chiefly on indirect, but apparently trustworthy, evidence +that the slopes of the old embankments are the same as they +originally were; and it is obvious that he could know nothing about +their original heights. In Knole Park a mound had been thrown up +behind the rifle-targets, which appeared to have been formed of +earth originally supported by square blocks of turf. The sides +sloped, as nearly as I could estimate them, at an angle of 45 +degrees or 50 degrees with the horizon, and they were covered, +especially on the northern side, with long coarse grass, beneath +which many worm-castings were found. These had flowed bodily +downwards, and others had rolled down as pellets. Hence it is +certain that as long as a mound of this kind is tenanted by worms, +its height will be continually lowered. The fine earth which flows +or rolls down the sides of such a mound accumulates at its base in +the form of a talus. A bed, even a very thin bed, of fine earth is +eminently favourable for worms; so that a greater number of +castings would tend to be ejected on a talus thus formed than +elsewhere; and these would be partially washed away by every heavy +shower and be spread over the adjoining level ground. The final +result would be the lowering of the whole mound, whilst the +inclination of the sides would not be greatly lessened. The same +result would assuredly follow with ancient embankments and tumuli; +except where they had been formed of gravel or of nearly pure sand, +as such matter is unfavourable for worms. Many old fortifications +and tumuli are believed to be at least 2000 years old; and we +should bear in mind that in many places about one inch of mould is +brought to the surface in 5 years or two inches in 10 years. +Therefore in so long a period as 2000 years, a large amount of +earth will have been repeatedly brought to the surface on most old +embankments and tumuli, especially on the talus round their bases, +and much of this earth will have been washed completely away. We +may therefore conclude that all ancient mounds, when not formed of +materials unfavourable to worms, will have been somewhat lowered in +the course of centuries, although their inclinations may not have +been greatly changed. + +Fields formerly ploughed.--From a very remote period and in many +countries, land has been ploughed, so that convex beds, called +crowns or ridges, usually about 8 feet across and separated by +furrows, have been thrown up. The furrows are directed so as to +carry off the surface water. In my attempts to ascertain how long +a time these crowns and furrows last, when ploughed land has been +converted into pasture, obstacles of many kinds were encountered. +It is rarely known when a field was last ploughed; and some fields +which were thought to have been in pasture from time immemorial +were afterwards discovered to have been ploughed only 50 or 60 +years before. During the early part of the present century, when +the price of corn was very high, land of all kinds seems to have +been ploughed in Britain. There is, however, no reason to doubt +that in many cases the old crowns and furrows have been preserved +from a very ancient period. {81} That they should have been +preserved for very unequal lengths of time would naturally follow +from the crowns, when first thrown up, having differed much in +height in different districts, as is now the case with recently +ploughed land. + +In old pasture fields, the mould, wherever measurements were made, +was found to be from 0.5 to 2 inches thicker in the furrows than on +the crowns; but this would naturally follow from the finer earth +having been washed from the crowns into the furrows before the land +was well clothed with turf; and it is impossible to tell what part +worms may have played in the work. Nevertheless from what we have +seen, castings would certainly tend to flow and to be washed during +heavy rain from the crowns into the furrows. But as soon as a bed +of fine earth had by any means been accumulated in the furrows, it +would be more favourable for worms than the other parts, and a +greater number of castings would be thrown up here than elsewhere; +and as the furrows on sloping land are usually directed so as to +carry off the surface water, some of the finest earth would be +washed from the castings which had been here ejected and be carried +completely away. The result would be that the furrows would be +filled up very slowly, while the crowns would be lowered perhaps +still more slowly by the flowing and rolling of the castings down +their gentle inclinations into the furrows. + +Nevertheless it might be expected that old furrows, especially +those on a sloping surface, would in the course of time be filled +up and disappear. Some careful observers, however, who examined +fields for me in Gloucestershire and Staffordshire could not detect +any difference in the state of the furrows in the upper and lower +parts of sloping fields, supposed to have been long in pasture; and +they came to the conclusion that the crowns and furrows would last +for an almost endless number of centuries. On the other hand the +process of obliteration seems to have commenced in some places. +Thus in a grass field in North Wales, known to have been ploughed +about 65 years ago, which sloped at an angle of 15 degrees to the +north-east, the depth of the furrows (only 7 feet apart) was +carefully measured, and was found to be about 4.5 inches in the +upper part of the slope, and only 1 inch near the base, where they +could be traced with difficulty. On another field sloping at about +the same angle to the south-west, the furrows were scarcely +perceptible in the lower part; although these same furrows when +followed on to some adjoining level ground were from 2.5 to 3.5 +inches in depth. A third and closely similar case was observed. +In a fourth case, the mould in a furrow in the upper part of a +sloping field was 2.5 inches, and in the lower part 4.5 inches in +thickness. + +On the Chalk Downs at about a mile distance from Stonehenge, my son +William examined a grass-covered, furrowed surface, sloping at from +8 degrees to 10 degrees, which an old shepherd said had not been +ploughed within the memory of man. The depth of one furrow was +measured at 16 points in a length of 68 paces, and was found to be +deeper where the slope was greatest and where less earth would +naturally tend to accumulate, and at the base it almost +disappeared. The thickness of the mould in this furrow in the +upper part was 2.5 inches, which increased to 5 inches, a little +above the steepest part of the slope; and at the base, in the +middle of the narrow valley, at a point which the furrow if +continued would have struck, it amounted to 7 inches. On the +opposite side of the valley, there were very faint, almost +obliterated, traces of furrows. Another analogous but not so +decided a case was observed at a few miles' distance from +Stonehenge. On the whole it appears that the crowns and furrows on +land formerly ploughed, but now covered with grass, tend slowly to +disappear when the surface is inclined; and this is probably in +large part due to the action of worms; but that the crowns and +furrows last for a very long time when the surface is nearly level. + +Formation and amount of mould over the Chalk Formation.--Worm- +castings are often ejected in extraordinary numbers on steep, +grass-covered slopes, where the Chalk comes close to the surface, +as my son William observed near Winchester and elsewhere. If such +castings are largely washed away during heavy rains, it is +difficult to understand at first how any mould can still remain on +our Downs, as there does not appear any evident means for supplying +the loss. There is, moreover, another cause of loss, namely, in +the percolation of the finer particles of earth into the fissures +in the chalk and into the chalk itself. These considerations led +me to doubt for a time whether I had not exaggerated the amount of +fine earth which flows or rolls down grass-covered slopes under the +form of castings; and I sought for additional information. In some +places, the castings on Chalk Downs consist largely of calcareous +matter, and here the supply is of course unlimited. But in other +places, for instance on a part of Teg Down near Winchester, the +castings were all black and did not effervesce with acids. The +mould over the chalk was here only from 3 to 4 inches in thickness. +So again on the plain near Stonehenge, the mould, apparently free +from calcareous matter, averaged rather less than 3.5 inches in +thickness. Why worms should penetrate and bring up chalk in some +places and not in others I do not know. + +In many districts where the land is nearly level, a bed several +feet in thickness of red clay full of unworn flints overlies the +Upper Chalk. This overlying matter, the surface of which has been +converted into mould, consists of the undissolved residue from the +chalk. It may be well here to recall the case of the fragments of +chalk buried beneath worm-castings on one of my fields, the angles +of which were so completely rounded in the course of 29 years that +the fragments now resembled water-worn pebbles. This must have +been effected by the carbonic acid in the rain and in the ground, +by the humus-acids, and by the corroding power of living roots. +Why a thick mass of residue has not been left on the Chalk, +wherever the land is nearly level, may perhaps be accounted for by +the percolation of the fine particles into the fissures, which are +often present in the chalk and are either open or are filled up +with impure chalk, or into the solid chalk itself. That such +percolation occurs can hardly be doubted. My son collected some +powdered and fragmentary chalk beneath the turf near Winchester; +the former was found by Colonel Parsons, R. E., to contain 10 per +cent., and the fragments 8 per cent. of earthy matter. On the +flanks of the escarpment near Abinger in Surrey, some chalk close +beneath a layer of flints, 2 inches in thickness and covered by 8 +inches of mould, yielded a residue of 3.7 per cent. of earthy +matter. On the other hand the Upper Chalk properly contains, as I +was informed by the late David Forbes who had made many analyses, +only from 1 to 2 per cent. of earthy matter; and two samples from +pits near my house contained 1.3 and 0.6 per cent. I mention these +latter cases because, from the thickness of the overlying bed of +red clay with flints, I had imagined that the underlying chalk +might here be less pure than elsewhere. The cause of the residue +accumulating more in some places than in others, may be attributed +to a layer of argillaceous matter having been left at an early +period on the chalk, and this would check the subsequent +percolation of earthy matter into it. + +From the facts now given we may conclude that castings ejected on +our Chalk Downs suffer some loss by the percolation of their finer +matter into the chalk. But such impure superficial chalk, when +dissolved, would leave a larger supply of earthy matter to be added +to the mould than in the case of pure chalk. Besides the loss +caused by percolation, some fine earth is certainly washed down the +sloping grass-covered surfaces of our Downs. The washing-down +process, however, will be checked in the course of time; for +although I do not know how thin a layer of mould suffices to +support worms, yet a limit must at last be reached; and then their +castings would cease to be ejected or would become scanty. + +The following cases show that a considerable quantity of fine earth +is washed down. The thickness of the mould was measured at points +12 yards apart across a small valley in the Chalk near Winchester. +The sides sloped gently at first; then became inclined at about 20 +degrees; then more gently to near the bottom, which transversely +was almost level and about 50 yards across. In the bottom, the +mean thickness of the mould from five measurements was 8.3 inches; +whilst on the sides of the valley, where the inclination varied +between 14 degrees and 20 degrees, its mean thickness was rather +less than 3.5 inches. As the turf-covered bottom of the valley +sloped at an angle of only between 2 degrees and 3 degrees, it is +probable that most of the 8.3-inch layer of mould had been washed +down from the flanks of the valley, and not from the upper part. +But as a shepherd said that he had seen water flowing in this +valley after the sudden thawing of snow, it is possible that some +earth may have been brought down from the upper part; or, on the +other hand, that some may have been carried further down the +valley. Closely similar results, with respect to the thickness of +the mould, were obtained in a neighbouring valley. + +St. Catherine's Hill, near Winchester, is 327 feet in height, and +consists of a steep cone of chalk about 0.25 of a mile in diameter. +The upper part was converted by the Romans, or, as some think, by +the ancient Britons, into an encampment, by the excavation of a +deep and broad ditch all round it. Most of the chalk removed +during the work was thrown upwards, by which a projecting bank was +formed; and this effectually prevents worm-castings (which are +numerous in parts), stones, and other objects from being washed or +rolled into the ditch. The mould on the upper and fortified part +of the hill was found to be in most places only from 2.5 to 3.5 +inches in thickness; whereas it had accumulated at the foot of the +embankment above the ditch to a thickness in most places of from 8 +to 9.5 inches. On the embankment itself the mould was only 1 to +1.5 inch in thickness; and within the ditch at the bottom it varied +from 2.5 to 3.5, but was in one spot 6 inches in thickness. On the +north-west side of the hill, either no embankment had ever been +thrown up above the ditch, or it had subsequently been removed; so +that here there was nothing to prevent worm-castings, earth and +stones being washed into the ditch, at the bottom of which the +mould formed a layer from 11 to 22 inches in thickness. It should +however be stated that here and on other parts of the slope, the +bed of mould often contained fragments of chalk and flint which had +obviously rolled down at different times from above. The +interstices in the underlying fragmentary chalk were also filled up +with mould. + +My son examined the surface of this hill to its base in a south- +west direction. Beneath the great ditch, where the slope was about +24 degrees, the mould was very thin, namely, from 1.5 to 2.5 +inches; whilst near the base, where the slope was only 3 degrees to +4 degrees, it increased to between 8 and 9 inches in thickness. We +may therefore conclude that on this artificially modified hill, as +well as in the natural valleys of the neighbouring Chalk Downs, +some fine earth, probably derived in large part from worm-castings, +is washed down, and accumulates in the lower parts, notwithstanding +the percolation of an unknown quantity into the underlying chalk; a +supply of fresh earthy matter being afforded by the dissolution of +the chalk through atmospheric and other agencies. + + + +CHAPTER VII--CONCLUSION. + + + +Summary of the part which worms have played in the history of the +world--Their aid in the disintegration of rocks--In the denudation +of the land--In the preservation of ancient remains--In the +preparation of the soil for the growth of plants--Mental powers of +worms--Conclusion. + +Worms have played a more important part in the history of the world +than most persons would at first suppose. In almost all humid +countries they are extraordinarily numerous, and for their size +possess great muscular power. In many parts of England a weight of +more than ten tons (10,516 kilogrammes) of dry earth annually +passes through their bodies and is brought to the surface on each +acre of land; so that the whole superficial bed of vegetable mould +passes through their bodies in the course of every few years. From +the collapsing of the old burrows the mould is in constant though +slow movement, and the particles composing it are thus rubbed +together. By these means fresh surfaces are continually exposed to +the action of the carbonic acid in the soil, and of the humus-acids +which appear to be still more efficient in the decomposition of +rocks. The generation of the humus-acids is probably hastened +during the digestion of the many half-decayed leaves which worms +consume. Thus the particles of earth, forming the superficial +mould, are subjected to conditions eminently favourable for their +decomposition and disintegration. Moreover, the particles of the +softer rocks suffer some amount of mechanical trituration in the +muscular gizzards of worms, in which small stones serve as mill- +stones. + +The finely levigated castings, when brought to the surface in a +moist condition, flow during rainy weather down any moderate slope; +and the smaller particles are washed far down even a gently +inclined surface. Castings when dry often crumble into small +pellets and these are apt to roll down any sloping surface. Where +the land is quite level and is covered with herbage, and where the +climate is humid so that much dust cannot be blown away, it appears +at first sight impossible that there should be any appreciable +amount of sub-aerial denudation; but worm-castings are blown, +especially whilst moist and viscid, in one uniform direction by the +prevalent winds which are accompanied by rain. By these several +means the superficial mould is prevented from accumulating to a +great thickness; and a thick bed of mould checks in many ways the +disintegration of the underlying rocks and fragments of rock. + +The removal of worm-castings by the above means leads to results +which are far from insignificant. It has been shown that a layer +of earth, 0.2 of an inch in thickness, is in many places annually +brought to the surface; and if a small part of this amount flows, +or rolls, or is washed, even for a short distance, down every +inclined surface, or is repeatedly blown in one direction, a great +effect will be produced in the course of ages. It was found by +measurements and calculations that on a surface with a mean +inclination of 9 degrees 26 seconds, 2.4 cubic inches of earth +which had been ejected by worms crossed, in the course of a year, a +horizontal line one yard in length; so that 240 cubic inches would +cross a line 100 yards in length. This latter amount in a damp +state would weigh 11.5 pounds. Thus a considerable weight of earth +is continually moving down each side of every valley, and will in +time reach its bed. Finally this earth will be transported by the +streams flowing in the valleys into the ocean, the great receptacle +for all matter denuded from the land. It is known from the amount +of sediment annually delivered into the sea by the Mississippi, +that its enormous drainage-area must on an average be lowered +.00263 of an inch each year; and this would suffice in four and +half million years to lower the whole drainage-area to the level of +the sea-shore. So that, if a small fraction of the layer of fine +earth, 0.2 of an inch in thickness, which is annually brought to +the surface by worms, is carried away, a great result cannot fail +to be produced within a period which no geologist considers +extremely long. + + +Archaeologists ought to be grateful to worms, as they protect and +preserve for an indefinitely long period every object, not liable +to decay, which is dropped on the surface of the land, by burying +it beneath their castings. Thus, also, many elegant and curious +tesselated pavements and other ancient remains have been preserved; +though no doubt the worms have in these cases been largely aided by +earth washed and blown from the adjoining land, especially when +cultivated. The old tesselated pavements have, however, often +suffered by having subsided unequally from being unequally +undermined by the worms. Even old massive walls may be undermined +and subside; and no building is in this respect safe, unless the +foundations lie 6 or 7 feet beneath the surface, at a depth at +which worms cannot work. It is probable that many monoliths and +some old walls have fallen down from having been undermined by +worms. + + +Worms prepare the ground {82} in an excellent manner for the growth +of fibrous-rooted plants and for seedlings of all kinds. They +periodically expose the mould to the air, and sift it so that no +stones larger than the particles which they can swallow are left in +it. They mingle the whole intimately together, like a gardener who +prepares fine soil for his choicest plants. In this state it is +well fitted to retain moisture and to absorb all soluble +substances, as well as for the process of nitrification. The bones +of dead animals, the harder parts of insects, the shells of land- +molluscs, leaves, twigs, &c., are before long all buried beneath +the accumulated castings of worms, and are thus brought in a more +or less decayed state within reach of the roots of plants. Worms +likewise drag an infinite number of dead leaves and other parts of +plants into their burrows, partly for the sake of plugging them up +and partly as food. + +The leaves which are dragged into the burrows as food, after being +torn into the finest shreds, partially digested, and saturated with +the intestinal and urinary secretions, are commingled with much +earth. This earth forms the dark coloured, rich humus which almost +everywhere covers the surface of the land with a fairly well- +defined layer or mantle. Hensen {83} placed two worms in a vessel +18 inches in diameter, which was filled with sand, on which fallen +leaves were strewed; and these were soon dragged into their burrows +to a depth of 3 inches. After about 6 weeks an almost uniform +layer of sand, a centimeter (0.4 inch) in thickness, was converted +into humus by having passed through the alimentary canals of these +two worms. It is believed by some persons that worm-burrows, which +often penetrate the ground almost perpendicularly to a depth of 5 +or 6 feet, materially aid in its drainage; notwithstanding that the +viscid castings piled over the mouths of the burrows prevent or +check the rain-water directly entering them. They allow the air to +penetrate deeply into the ground. They also greatly facilitate the +downward passage of roots of moderate size; and these will be +nourished by the humus with which the burrows are lined. Many +seeds owe their germination to having been covered by castings; and +others buried to a considerable depth beneath accumulated castings +lie dormant, until at some future time they are accidentally +uncovered and germinate. + +Worms are poorly provided with sense-organs, for they cannot be +said to see, although they can just distinguish between light and +darkness; they are completely deaf, and have only a feeble power of +smell; the sense of touch alone is well developed. They can +therefore learn but little about the outside world, and it is +surprising that they should exhibit some skill in lining their +burrows with their castings and with leaves, and in the case of +some species in piling up their castings into tower-like +constructions. But it is far more surprising that they should +apparently exhibit some degrees of intelligence instead of a mere +blind instinctive impulse, in their manner of plugging up the +mouths of their burrows. They act in nearly the same manner as +would a man, who had to close a cylindrical tube with different +kinds of leaves, petioles, triangles of paper, &c., for they +commonly seize such objects by their pointed ends. But with thin +objects a certain number are drawn in by their broader ends. They +do not act in the same unvarying manner in all cases, as do most of +the lower animals; for instance, they do not drag in leaves by +their foot-stalks, unless the basal part of the blade is as narrow +as the apex, or narrower than it. + + +When we behold a wide, turf-covered expanse, we should remember +that its smoothness, on which so much of its beauty depends, is +mainly due to all the inequalities having been slowly levelled by +worms. It is a marvellous reflection that the whole of the +superficial mould over any such expanse has passed, and will again +pass, every few years through the bodies of worms. The plough is +one of the most ancient and most valuable of man's inventions; but +long before he existed the land was in fact regularly ploughed, and +still continues to be thus ploughed by earth-worms. It may be +doubted whether there are many other animals which have played so +important a part in the history of the world, as have these lowly +organized creatures. Some other animals, however, still more lowly +organized, namely corals, have done far more conspicuous work in +having constructed innumerable reefs and islands in the great +oceans; but these are almost confined to the tropical zones. + + + +Footnotes: + +{1} 'Lecons de Geologie Pratique,' tom. i. 1845, p. 140. + +{2} 'Transactions Geolog. Soc.' vol. v. p. 505. Read November 1, +1837. + +{3} 'Histoire des progres de la Geologie,' tom. i. 1847, p. 224. + +{4} 'Zeitschrift fur wissenschaft. Zoologie,' B. xxviii. 1877, p. +361. + +{5} 'Gardeners' Chronicle,' April 17, 1869, p. 418. + +{6} Mr. Darwin's attention was called by Professor Hensen to P. E. +Muller's work on Humus in 'Tidsskrift for Skovbrug,' Band iii. Heft +1 and 2, Copenhagen, 1878. He had, however, no opportunity of +consulting Muller's work. Dr. Muller published a second paper in +1884 in the same periodical--a Danish journal of forestry. His +results have also been published in German, in a volume entitled +'Studien uber die naturlichen Humusformen, unter deren Einwirkung +auf Vegetation und Boden,' 8vo., Berlin, 1887. + +{7} 'Bidrag till Skandinaviens Oligochaetfauna,' 1871. + +{8} 'Die bis jetzt bekannten Arten aus der Familie der +Regenwurmer,' 1845. + +{9} There is even some reason to believe that pressure is actually +favourable to the growth of grasses, for Professor Buckman, who +made many observations on their growth in the experimental gardens +of the Royal Agricultural College, remarks ('Gardeners' Chronicle,' +1854, p. 619): "Another circumstance in the cultivation of grasses +in the separate form or small patches, is the impossibility of +rolling or treading them firmly, without which no pasture can +continue good." + +{10} I shall have occasion often to refer to M. Perrier's +admirable memoir, 'Organisation des Lombriciens terrestres' in +'Archives de Zoolog. exper.' tom. iii. 1874, p. 372. C. F. Morren +('De Lumbrici terrestris Hist. Nat.' 1829, p. 14) found that worms +endured immersion for fifteen to twenty days in summer, but that in +winter they died when thus treated. + +{11} Morren, 'De Lumbrici terrestris Hist. Nat.' &c., 1829, p. 67. + +{12} 'De Lumbrici terrestris Hist. Nat.' &c., p. 14. + +{13} Histolog. Untersuchungen uber die Regenwurmer. 'Zeitschrift +fur wissenschaft. Zoologie,' B. xix., 1869, p. 611. + +{14} For instance, Mr. Bridgman and Mr. Newman ('The Zoologist,' +vol. vii. 1849, p. 2576), and some friends who observed worms for +me. + +{15} 'Familie der Regenwurmer,' 1845, p. 18. + +{16} 'The Zoologist,' vol. vii. 1849, p. 2576. + +{17} 'Familie der Regenwurmer,' p. 13. Dr. Sturtevant states in +the 'New York Weekly Tribune' (May 19, 1880) that he kept three +worms in a pot, which was allowed to become extremely dry; and +these worms were found "all entwined together, forming a round mass +and in good condition." + +{18} 'De Lumbrici terrestris Hist. Nat.' p. 19. + +{19} 'Archives de Zoologie experimentale,' tom. vii. 1878, p. 394. +When I wrote the above passage, I was not aware that Krukenberg +('Untersuchungen a. d. physiol. Inst. d. Univ. Heidelberg,' Bd. +ii. p. 37, 1877) had previously investigated the digestive juice of +Lumbricus. He states that it contains a peptic, and diastatic, as +well as a tryptic ferment. + +{20} On the action of the pancreatic ferment, see 'A Text-Book of +Physiology,' by Michael Foster, 2nd edit. pp. 198-203. 1878. + +{21} Schmulewitsch, 'Action des Sucs digestifs sur la Cellulose.' +Bull. de l'Acad. Imp. de St. Petersbourg, tom. xxv. p. 549. 1879. + +{22} Claparede doubts whether saliva is secreted by worms: see +'Zeitschrift fur wissenschaft. Zoologie,' B. xix. 1869, p. 601. + +{23} Perrier, 'Archives de Zoolog. exper.' July, 1874, pp. 416, +419. + +{24} 'Zeitschrift fur wissenschaft. Zoologie,' B. xix, 1869, pp. +603-606. + +{25} De Vries, 'Landwirth. Jahrbucher,' 1881, p. 77. + +{26} M. Foster, 'A Text-Book of Physiology,' 2nd edit. 1878, p. +243. + +{27} M. Foster, ut sup. p. 200. + +{28} Claparede remarks ('Zeitschrift fur wisseuschaft. Zoolog.' +B. 19, 1869, p. 602) that the pharynx appears from its structure to +be adapted for suction. + +{29} An account of her observations is given in the 'Gardeners' +Chronicle,' March 28th, 1868, p. 324. + +{30} London's 'Gard. Mag.' xvii. p. 216, as quoted in the +'Catalogue of the British Museum Worms,' 1865, p. 327. + +{31} 'Familie der Regenwurmer,' p. 19. + +{32} In these narrow triangles the apical angle is 9 degrees 34 +seconds, and the basal angles 85 degrees 13 seconds. In the +broader triangles the apical angle is 19 degrees 10 seconds and the +basal angles 80 degrees 25 seconds. + +{33} See his interesting work, 'Souvenirs entomologiques,' 1879, +pp. 168-177. + +{34} Mobius, 'Die Bewegungen der Thiere,' &c., 1873, p. 111. + +{35} 'Annals and Mag. of N. History,' series ii. vol. ix. 1852, p. +333. + +{36} 'Archives de Zoolog. exper.' tom. iii. 1874, p. 405. + +{37} I state this on the authority of Semper, 'Reisen im Archipel +der Philippinen,' Th. ii. 1877, p. 30. + +{38} Dr. King gave me some worms collected near Nice, which, as he +believes, had constructed these castings. They were sent to M. +Perrier, who with great kindness examined and named them for me: +they consisted of Perichaeta affinis, a native of Cochin China and +of the Philippines; P. Luzonica, a native of Luzon in the +Philippines; and P. Houlleti, which lives near Calcutta. M. +Perrier informs me that species of Perichaeta have been naturalized +in the gardens near Montpellier and in Algiers. Before I had any +reason to suspect that the tower-like castings from Nice had been +formed by worms not endemic in the country, I was greatly surprised +to see how closely they resembled castings sent to me from near +Calcutta, where it is known that species of Perichaeta abound. + +{39} 'Zeitschrift fur wissenschaft. Zoolog.' B. xxviii. 1877, p. +364. + +{40} 'Zeitschrift fur wissenschaft. Zoolog.' B. xxviii. 1877, p. +356. + +{41} Perrier, 'Archives de Zoolog. exper.' tom. 3, p. 378, 1874. + +{42} This case is given in a postscript to my paper in the +'Transact. Geolog. Soc.' (Vol. v. p. 505), and contains a serious +error, as in the account received I mistook the figure 30 for 80. +The tenant, moreover, formerly said that he had marled the field +thirty years before, but was now positive that this was done in +1809, that is twenty-eight years before the first examination of +the field by my friend. The error, as far as the figure 80 is +concerned, was corrected in an article by me, in the 'Gardeners' +Chronicle,' 1844, p. 218. + +{43} These pits or pipes are still in process of formation. +During the last forty years I have seen or heard of five cases, in +which a circular space, several feet in diameter, suddenly fell in, +leaving on the field an open hole with perpendicular sides, some +feet in depth. This occurred in one of my own fields, whilst it +was being rolled, and the hinder quarters of the shaft horse fell +in; two or three cart-loads of rubbish were required to fill up the +hole. The subsidence occurred where there was a broad depression, +as if the surface had fallen in at several former periods. I heard +of a hole which must have been suddenly formed at the bottom of a +small shallow pool, where sheep had been washed during many years, +and into which a man thus occupied fell to his great terror. The +rain-water over this whole district sinks perpendicularly into the +ground, but the chalk is more porous in certain places than in +others. Thus the drainage from the overlying clay is directed to +certain points, where a greater amount of calcareous matter is +dissolved than elsewhere. Even narrow open channels are sometimes +formed in the solid chalk. As the chalk is slowly dissolved over +the whole country, but more in some parts than in others, the +undissolved residue--that is the overlying mass of red clay with +flints,--likewise sinks slowly down, and tends to fill up the pipes +or cavities. But the upper part of the red clay holds together, +aided probably by the roots of plants, for a longer time than the +lower parts, and thus forms a roof, which sooner or later falls in, +as in the above mentioned five cases. The downward movement of the +clay may be compared with that of a glacier, but is incomparably +slower; and this movement accounts for a singular fact, namely, +that the much elongated flints which are embedded in the chalk in a +nearly horizontal position, are commonly found standing nearly or +quite upright in the red clay. This fact is so common that the +workmen assured me that this was their natural position. I roughly +measured one which stood vertically, and it was of the same length +and of the same relative thickness as one of my arms. These +elongated flints must get placed in their upright position, on the +same principle that a trunk of a tree left on a glacier assumes a +position parallel to the line of motion. The flints in the clay +which form almost half its bulk, are very often broken, though not +rolled or abraded; and this may he accounted for by their mutual +pressure, whilst the whole mass is subsiding. I may add that the +chalk here appears to have been originally covered in parts by a +thin bed of fine sand with some perfectly rounded flint pebbles, +probably of Tertiary age; for such sand often partly fills up the +deeper pits or cavities in the chalk. + +{44} S. W. Johnson, 'How Crops Feed,' 1870, p. 139. + +{45} 'Nature,' November 1877, p. 28. + +{46} 'Proc. Phil. Soc.' of Manchester, 1877, p. 247. + +{47} 'Trans. of the New Zealand Institute,' vol. xii., 1880, p. +152. + +{48} Mr. Lindsay Carnagie, in a letter (June 1838) to Sir C. +Lyell, remarks that Scotch farmers are afraid of putting lime on +ploughed land until just before it is laid down for pasture, from a +belief that it has some tendency to sink. He adds: "Some years +since, in autumn, I laid lime on an oat-stubble and ploughed it +down; thus bringing it into immediate contact with the dead +vegetable matter, and securing its thorough mixture through the +means of all the subsequent operations of fallow. In consequence +of the above prejudice, I was considered to have committed a great +fault; but the result was eminently successful, and the practice +was partially followed. By means of Mr. Darwin's observations, I +think the prejudice will be removed." + +{49} This conclusion, which, as we shall immediately see, is fully +justified, is of some little importance, as the so-called bench- +stones, which surveyors fix in the ground as a record of their +levels, may in time become false standards. My son Horace intends +at some future period to ascertain how far this has occurred. + +{50} Mr. R. Mallet remarks ('Quarterly Journal of Geolog. Soc.' +vol. xxxiii., 1877, p. 745) that "the extent to which the ground +beneath the foundations of ponderous architectural structures, such +as cathedral towers, has been known to become compressed, is as +remarkable as it is instructive and curious. The amount of +depression in some cases may be measured by feet." He instances +the Tower of Pisa, but adds that it was founded on "dense clay." + +{51} 'Zeitschrift fur wissensch. Zoolog.' Bd. xxviii., 1877, p. +360. + +{52} See Mr. Dancer's paper in 'Proc. Phil. Soc. of Manchester,' +1877, p. 248. + +{53} 'Lecons de Geologie pratique,' 1845, p. 142. + +{54} A short account of this discovery was published in 'The +Times' of January 2, 1878; and a fuller account in 'The Builder,' +January 5, 1878. + +{55} Several accounts of these ruins have been published; the best +is by Mr. James Farrer in 'Proc. Soc. of Antiquaries of Scotland,' +vol. vi., Part II., 1867, p. 278. Also J. W. Grover, 'Journal of +the British Arch. Assoc.' June 1866. Professor Buckman has +likewise published a pamphlet, 'Notes on the Roman Villa at +Chedworth,' 2nd edit. 1873 Cirencester. + +{56} These details are taken from the 'Penny Cyclopaedia,' article +Hampshire. + +{57} "On the denudation of South Wales," &c., 'Memoirs of the +Geological Survey of Great Britain,' vol. 1., p. 297, 1846. + +{58} 'Geological Magazine,' October and November, 1867, vol. iv. +pp. 447 and 483. Copious references on the subject are given in +this remarkable memoir. + +{59} A. Tylor "On changes of the sea-level," &c., ' Philosophical +Mag.' (Ser. 4th) vol. v., 1853, p. 258. Archibald Geikie, +Transactions Geolog. Soc. of Glasgow, vol. iii., p. 153 (read +March, 1868). Croll "On Geological Time," 'Philosophical Mag.,' +May, August, and November, 1868. See also Croll, 'Climate and +Time,' 1875, Chap. XX. For some recent information on the amount +of sediment brought down by rivers, see 'Nature,' Sept. 23rd, +1880. Mr. T. Mellard Reade has published some interesting articles +on the astonishing amount of matter brought down in solution by +rivers. See Address, Geolog. Soc., Liverpool, 1876-77. + +{60} "An account of the fine dust which often falls on Vessels in +the Atlantic Ocean," Proc. Geolog. Soc. of London, June 4th, 1845. + +{61} For La Plata, see my 'Journal of Researches,' during the +voyage of the Beagle, 1845, p. 133. Elie de Beaumont has given +('Lecons de Geolog. pratique,' tom. I. 1845, p. 183) an excellent +account of the enormous quantity of dust which is transported in +some countries. I cannot but think that Mr. Proctor has somewhat +exaggerated ('Pleasant Ways in Science,' 1879, p. 379) the agency +of dust in a humid country like Great Britain. James Geikie has +given ('Prehistoric Europe,' 1880, p. 165) a full abstract of +Richthofen's views, which, however, he disputes. + +{62} These statements are taken from Hensen in 'Zeitschrift fur +wissenschaft. Zoologie.' Bd. xxviii., 1877, p. 360. Those with +respect to peat are taken from Mr. A. A. Julien in 'Proc. American +Assoc. Science,' 1879, p. 354. + +{63} I have given some facts on the climate necessary or +favourable for the formation of peat, in my 'Journal of +Researches,' 1845, p. 287. + +{64} A. A. Julien "On the Geological action of the Humus-acids," +'Proc. American Assoc. Science,' vol. xxviii., 1879, p. 311. Also +on "Chemical erosion on Mountain Summits;" 'New York Academy of +Sciences,' Oct. 14, 1878, as quoted in the 'American Naturalist.' +See also, on this subject, S. W. Johnson, 'How Crops Feed,' 1870, +p. 138. + +{65} See, for references on this subject, S. W. Johnson, 'How +Crops Feed,' 1870, p. 326. + +{66} This statement is taken from Mr. Julien, 'Proc. American +Assoc. Science,' vol. xxviii., 1879, p. 330. + +{67} The preservative power of a layer of mould and turf is often +shown by the perfect state of the glacial scratches on rocks when +first uncovered. Mr. J. Geikie maintains, in his last very +interesting work ('Prehistoric Europe,' 1881), that the more +perfect scratches are probably due to the last access of cold and +increase of ice, during the long-continued, intermittent glacial +period. + +{68} Many geologists have felt much surprise at the complete +disappearance of flints over wide and nearly level areas, from +which the chalk has been removed by subaerial denudation. But the +surface of every flint is coated by an opaque modified layer, which +will just yield to a steel point, whilst the freshly fractured, +translucent surface will not thus yield. The removal by +atmospheric agencies of the outer modified surfaces of freely +exposed flints, though no doubt excessively slow, together with the +modification travelling inwards, will, as may be suspected, +ultimately lead to their complete disintegration, notwithstanding +that they appear to be so extremely durable. + +{69} 'Archives de Zoolog. exper.' tom. iii. 1874, p. 409. + +{70} 'Nouvelles Archives du Museum,' tom. viii. 1872, pp. 95, +131. + +{71} Morren, in speaking of the earth in the alimentary canals of +worms, says, "praesepe cum lapillis commixtam vidi:" 'De Lumbrici +terrestris Hist. Nat.' &c., 1829, p. 16. + +{72} Perrier, 'Archives de Zoolog. exper.' tom. iii. 1874, p. 419. + +{73} Morren, 'De Lumbrici terrestris Hist. Nat.' &c., p. 16. + +{74} 'Archives de Zoolog. exper.' tom. iii. 1874, p. 418. + +{75} This conclusion reminds me of the vast amount of extremely +fine chalky mud which is found within the lagoons of many atolls, +where the sea is tranquil and waves cannot triturate the blocks of +coral. This mud must, as I believe ('The Structure and +Distribution of Coral-Reefs,' 2nd edit. 1874, p. 19), be attributed +to the innumerable annelids and other animals which burrow into the +dead coral, and to the fishes, Holothurians, &c., which browse on +the living corals. + +{76} Anniversary Address: 'The Quarterly Journal of the +Geological Soc.' May 1880, p. 59. + +{77} Mr. James Wallace has pointed out that it is necessary to +take into consideration the possibility of burrows being made at +right angles to the surface instead of vertically down, in which +case the lateral displacement of the soil would be increased. + +{78} 'Elements of Geology,' 1865, p. 20. + +{79} 'Lecons de Geologie pratique, 1845; cinquieme Lecon. All +Elie de Beaumont's arguments are admirably controverted by Prof. A. +Geikie in his essay in Transact. Geolog. Soc. of Glasgow, vol. iii. +p. 153, 1868. + +{80} 'Illustrations of the Huttonian Theory of the Earth,' p. 107. + +{81} Mr. E. Tylor in his Presidential address ('Journal of the +Anthropological Institute,' May 1880, p. 451) remarks: "It appears +from several papers of the Berlin Society as to the German 'high- +fields' or 'heathen-fields' (Hochacker, and Heidenacker) that they +correspond much in their situation on hills and wastes with the +'elf-furrows' of Scotland, which popular mythology accounts for by +the story of the fields having been put under a Papal interdict, so +that people took to cultivating the hills. There seems reason to +suppose that, like the tilled plots in the Swedish forest which +tradition ascribes to the old 'hackers,' the German heathen-fields +represent tillage by an ancient and barbaric population." + +{82} White of Selborne has some good remarks on the service +performed by worms in loosening, &c., the soil. Edit, by L. +Jenyns, 1843, p. 281. + +{83} 'Zeitschrift fur wissenschaft. Zoolog.' B. xxviii. 1877, p. +360. + + + + + +End of the Project Gutenberg eText Vegetable Mould and Earth-Worms +**Project Gutenberg Etext Formation of Vegetable Mould, by Darwin + diff --git a/old/vgmld10.zip b/old/vgmld10.zip Binary files differnew file mode 100644 index 0000000..64e52a9 --- /dev/null +++ b/old/vgmld10.zip |