EARTH-WORMS AND THEIR WORKS. 295 



mold .iiul turf. But the smaller stones disappeared before many yens 

 had elapsed, as did every one of the larger ones after a time ; so 

 that after thirty years, or in 1871, a horse could gallop over the com- 

 pact turf from one end of the field to the other, and not strike a single 

 stone with his shoes. This, says Mr. Darwin, " 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 in- 

 creased in numbers as the pasture improved." The accumulation of 

 mold was, however, of the slowest, measuring only .083 of an inch a 

 year. A flagged path in Mr. Darwin's garden disappeared in the 

 course of years, it might be said under his very eyes, the worms cov- 

 ering it with an inch of mold. 



A stone, sixty-four inches long, seventeen inches broad, and from 

 nine to ten inches thick, part of the ruins of a lime-kiln that had been 

 torn down thirty-five years before, lay in a field, its base sunk from 

 one to two inches below the general level, while the surface of the 

 field for about nine inches around it sloped up toward it to the height 

 of four inches above the surrounding ground close to the stone. The 

 stone could not have sunk by its weight, and there was evidence that 

 one of its pointed ends, the upper surface of which was now on a level 

 with the surrounding turf, must have stood clear of the ground for 

 several inches. The situation of the stone is represented in Fig. 4. 



^ 



'x 7 ig. 4. Transverse Section across a Large Stone wic.cn had lain on a Grass-Field for 

 Thirtt-five Years. A A, general level of the field. The underlying brick rubbish has not 

 been represented. Scale one half inch to one foot. 



"When the stone was removed, an exact cast of its lower side, form- 

 ing a shallow crateriform hollow, was left, the inner surface of which, 

 except where the base had been in contact with brick rubbish, consisted 

 of fine black mold. The tm-f-covered border, which sloped up to the 

 stone, consisted of fine vegetable mold, in one part seven inches thick, 

 and was evidently derived from worm-castings, several of which had 

 been recently ejected. This stone would have sunk to the level of 

 the field in two hundred and forty-seven years if none of the castings 

 were washed away by rains. 



Some of the fallen stones at Stonehenge have become buried to a 

 moderate depth in the ground, and are surrounded by sloping borders 

 of turf, on which recent castings were seen. In the case of the stone 

 represented in the cut (Fig. 5), which is by no means the most marked 

 specimen, the turf -covered border sloped on one side to the height of 



