The Formation of Vegetable Mould through the Action of Worms

tained 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, [ 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 percola- tion, some fine earth is certainly washed down the sloping grass-covered surfaces of our Downs. The washing-down process, how- ever, 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 caste

The following cases show that a consider- able 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°; 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° and 20°, its mean thick- ness was rather less than 3°5 inches. As the turf-covered bottom of the valley sloped at an angle of only between 2° and 8°, 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 flow- ing 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. Ciosely 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 + 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 24 to 34 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 92 iuches. On the embankment itself the mould was only 1 to 14 inch in thickness; and within the ditch at the bottom it varied from 24 to 34, but was in one spot 6 inches in

thickness. On the north-west side of the hill, either nu embankment had ever been thrown up above the ditch, or it had subse- quently 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 con- tained fragments of chalk and flint which had obviously rolled down at different times from above. The interstices in the under- lying fraginentary 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°, the mould was very thin, namely from 13 to 23 inches; whilst near the base, where the slope was only 3° to 4°, 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 worm-castings, is washed down, and accumu- lates 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 o. the chalk through atmospheric and other agencies.

Summary of the part which worms have played in the history of the world—Their aid in the disintegration of rocks—lIn the denudation of the land—In the preservation of ancient remains —lIn the preparation of the soil for the growth of plants— Mental powers of worms—Concl sion. 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 sur- faces 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 giz- zards 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 im- possible that there should be any appreciable amount of subaerial 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 oreat 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, ‘2 of an inch in thickness, is in many plaves annually brought to the surface per acre; 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° 26’, 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 114 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 trom the amount of sediment annually delivered into the sea by the Mississippi, that its enormous drainage-area must on an aver- aye 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, 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 ex- tremely long.

Archeologists 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 trom the adjoining land, especially when cul- tivated. 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 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 par- ticles 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 nitri- - fication. 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 uumber of dead leaves and other parts of vlants into their burrows, partly for the sake of plugging them up and partly as food.

The leaves which are dragged into the bur- rows as food, after being torn into the finest shreds, partially digested, and saturated with the intestinal and urinary secretions, are com- mingled 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. Von Hensen* placed two worms in a vessel 18 inches in diameter, which was filled with sand, on which fallen leaves were strewed ; und these were soon dragged into their bur- rows to a depth of 3 inches. After about 6 weeks an almost uniform layer of sand, a centimeter (‘4 inch) in thickness, was con- verted 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; notwith- standing 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 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 ap- parently exhibit some degree 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, &e., 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 smooth- ness, on which so much of its beauty depends, is mainly due to all the inequalities having been slowly levelled by worms. It is a mar- vellous reflection that the whole of the super- ficial 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 organised creatures. Some other animals, however, still more lowly organised, 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,

ae 7 ae ‘ bey. cere a) ate picid: Roost at pha fie ay Apts ; cael ‘ i ss Sty Toe é on Jaigage r . all 3 ’ oa fA i? yeas os ere ee To j . 1 i 4 BAY * 7 ae ig a ; Eapcrk Vide Smee eee fee lon vue y t lta ¢ SMU) S ‘fant aoa rv huge An Nee phe aap ae a A" ty * ites ai ae ates eterertey 7 (75 «| SRM P ety | Beep Ree FY 40 chants getresan ye = Wide nivatinned y ete 7 _ » i, ; ie acer ners neneadietetlt p25 eer Th a, aye at ty is aati ———_ —- the transport of dust, 237 the permanence of mould, 289 a the permanence of ancient tumuli, 290 Beech-forests, stones not buried under by castings, 144 Bengal, worms of, 123 Bones, crushed, burial of, under castings, 146 Brading, Roman villa at, 199

Bridgman, Mr., on worms eating leaves of a Phlox, 33 Buckman, on grasses profiting by being rolled, 10 Burial of the remains of ancient buildings by worms, Burrows, depth of, 109 direction of, on a slope, 270 ——— excavation of, 98 lined with black earth, 111 lined with leaves, 112 mouths of, worms lie motionless near, 15 ———— old, their collapse, 118 plugged up, 58 ——-—— terminating in a small chamber, often lined with stones or seeds, 114 ejection of, 116 ———— tower-like, from near Calcutta, 123 of great size on the Nilgiri Mountains, 126 weight of, from a single burrow and from a given

thickness of layer formed from, during a year, 169 ——— ejected over ancient buildings, 253 ———— flowing down slopes, 261 ——— washed away, 272 ——— dry, disintegration of, 275 blown to leeward, 283 Cells, free, with calcareous matter in the calciferous Decay of leaves not hastened by the secretion with which _ they are bathed, 38 Down, amount of earth here brought annually to the surface, 137 acted on externally and internally by atmospherio agencies, 245

Food of worms, leaves, 35 earth, 100 Foster, Michael, on the pancreatic ferment, 37 on the acidity of the contents of the Galton, Mr., on the number of dead worms, 14 Geikie, Archibald, on Denudation, 233 controverts EK. de Beaumont’s views on , James, controverts Richthofen’s views, 237 _ on glaciated rocks, 245 Geographical distribution of worms, 120 Haast, Von, on aboriginal instruments in New Zealand found buried, 147 Heaths, inhabited by few worms, except where paths cross them, 10

Henslow, Prof., on ledges on hill-sides, 278 Hoffmeister, number of species of worms, 9 on worms hybernating in company, 34 perception of light by worms, 20, 22 Hooker, Sir J., on ledges of earth on the Himalaya, 278 Humus acids, action of on rocks, 240, 244 Intestines of worms, their contents acid, 51 Islands, inhabited by worms, 120 Joyce, Rey. J.G., on the Roman remains at Silchester, 201 Julien, Mr. A. A., on the composition of peat, 238 Key, Rev. H., on the burial of cinders by worms, 146 King, Dr., on the formation of mould in forests in France, 5

on castings near Nice, 106, 117 on great castings on the Nilgiri Mountaius and in Ceylon, 126 weight of castings near Nice, 163 on disintegrated castings on: the Corniche road, 276, 281 on the washing away of the castings on the Nilgiri Mountains, 274 Knole Park, beech-woods, worms absent, 12 Koninck, De, on the disintegration of rocks, 235 Leaves, worms distinguish the taste of different kinds, 32 consumed by worms, 35 their decay not hastened by the alkaline secretion with which they are bathed, 38

Ledges of earth on hill-sides, 278 , Léon, F., on the digestive fluid of worms, 38 Mallett, Mr., on the sinking of the ground under great buildings, 158 Nice, castings near, 106 disintegrated castings near, 276 Night, worms leave their burrows, 14 Nilgiri Mountains, castings on, 126 Objects strewed on the surface soon buried under cast ings, 130 Pavement, modern, undermined by worms, 192 Pavements, ancient, subsidence of, at Silchester, 212 Peat, formation of, 239

Pine-leaves used in plugging up burrows, 58, 70 lining burrows, 112 Remains, ancient, buried by worms, 176 Rhododendron leaves, 69 Richthofen on dust deposits in China, 237 Robinia, petioles of, 81 Rocks, disintegration of, aided by worms,»240 triturated in the gizzards of worms, 249 Rolling down of dry castings, 275 Romanes, Mr., on the intelligence of animals, 95 Sorby, Mr., on the trituration of small particles of rock, 257 Stones, great, undermined by worms at Leith Hill and at Stonehenge, 148

circular trenches near, 287 Structure of worms, 16 Subsidence of the pavements at Silchester, 212 Suction, power,of, 56 Sugar eaten by worms, 36 Summary of whole book, 305 Surface, objects strewed on, buried under castings, 130 Taste, power of, 32 Thickness of the layer of mould annually ejected by worms, 169 of the mould over the remains at Chedworth, 199 of the mould over the remains at Silchester, 218 of the mould over the Roman remains at Wroxeter, 223 Thyme, leaves of, not eaten by worms, 33 Touch, worms highly sensitive to, 28 Triangles of paper, 82 Trituration of particles of rock in the gizzards of worms, Tumuli, ancient, 290 Tylor, Mr. A., on Denudation, 233 Tylor, Mr. E., on anciently ploughed land, 293 Typhosolis, 19

Vibrations, worms sensitive to, 27 Vision, power of, in worms, 20 Wedgwood, Mr., on the formation of mould, 3 Weight of earth ejected from a single burrow, 160 Whitaker, Mr., on Denudation, 232 White, on worms leaving their burrows at night, 14 Winchester, chalk formation near, 301 formation of their burrows, 98 number of, living in a given area, 158 penetrating ancient walls, 188, 209 gizzards of, and the trituration of the contained stones, 246

prefer to live in fine earth, 291 Wright, Mr., on the age of Wroxeter, 221 Wroxeter, old Roman town of, 221