The Formation of Vegetable Mould through the Action of Worms

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 Jand, 16°1 tons of annually ejected dry earth.

(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 45 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, [ wished to learn how thick a layer of ordinary mould this amount would form if spread uni- formly 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 col- lected on the Terrace amounted to 124:77 cubic inches; and this amount, if spread out over a square yard, would make a layer °09612 inch in thickness. Those collected on the Common amounted to 197°56 cubie inches, and would make a similar layer *1524 inch in thickness.

These thicknesses must, however, be cor- rected, 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 com- pact, as is shown by the number of air- bubbles which rise up when the surface is flooded with water. It is moreover pene- trated by many fine roots. To ascertain ap- proximately 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 + 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 yy 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 5; and this will reduce the layer to ‘09 of an inch, so that a

layer °9 inch in thickness would be formed in the course of ten years. On the same prin- ciple the castings from the Common would make in the course of a single year a layer ‘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 14 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 :—

The accumulation of mould during 14% years on the surface of a dry, sandy, grass-field near Maer Hall, amounted to 2°2 inches in 10 years. The accumulation during 213 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 inches 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 under- gone through being washed by rain, by the adhesion of particles to the blades of the sur- rounding 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 larvee and insects, espe- cially 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 coun- tries, 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 greatroads. But in our county 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 ayear. 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 vunces, we may infer that the worms which live in an acre of pasture land must be less than 26,886 in number.

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 sub- soil 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 ata slower and slower rate, a thick- ness 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 débris, 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 cast- ings ejected within a known time on a measured space—will hereafter, as I believe, doubt that worms play an important part in nature.

The accumulation of rubbish on the sites of great cities inde- pendent 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 débris by which the remains are covered—The penetration of the tesselated floors aud 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.

ARCHAOLOGISTS are probably not aware how much they owe to worms for the preservation of many ancient objects. Coins, gold orna- ments, 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 con- sider 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 matériaux “ quien sort, on y en fait entrer cent.” * 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 25 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 tesserz (small red tiles), and surrounded on two sides by broken- down walls, was soon discovered. It is believed + 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

¢ 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. Roman emperors, dating from 133 to 361, and perhaps to 375 A.p., were likewise found. Also a halfpenny of George 1. 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 angie of about 7°; 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 315 0f 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

Section through the foundations of a buried Roman villa at Abinger. A A, vegetable mould; B, dark earth full of stones, 13 inches in thickness; C, black mould; D, broken mortar ; E, black mould; F F, undisturbed sub-soil; G, tessere ; H. concrete 1, nature unknown; W, buried wall. of the atrium varied in thickness ‘rom 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°, and in one place near the outside at as much as 8° 30" 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, bemg 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) (F) 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 63 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 other- wise the rotten concrete floor would have been scored by the ploughshare, the tesserz torn up, and the tops of the old walls knocked down.

When the concrete and tessere 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 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 cast- ings. 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 conclu- sion 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 pene- trated 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 tle interstices of the tesseree. 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 483, and another at 513 inches beneath the surface. A fresh humus-lined burrow was also met with at a depth of 57 and another at 643 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 work- ing 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 sur- face of the floor, and five or six vermiforim 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 neighbour- ing 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. The number of castings on the surrounding fields was now very large. Sept. 22nd ; 43 holes, only a few fresh castings ; all defaced. 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 Septem- ber 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 wa 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 sol 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 prob- able were formerly as numerous as they now are, had not collapsed in the course of time in the manner formerly explained, the under- lying earth would have been riddled with pas- sages like a sponge; and as this was not the case, we may feel sure that they have collapsed. The inevitable result of such col- lapsing during successive centuries, will have been the slow subsidence of the floor and of the walls, and their burial beneath the accumu- lated 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. Hven those parts of the coucrete 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 dif- ferent 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 accumu- lated over the ruins than that now present. But beside the castings of worms and some

earth brought up by insects, and some accu- mulation 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 thick- ness 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 pave- ment 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. Con- sidering 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—mThis 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