The estimates of the amount of mold brought up by the worms, based on actual weighings and measurements of the castings at particular spots, give results ranging from 7·56 to 15·12 tons per acre in one year, and a volume sufficient to make when spread out a layer of soil of from one to more than two inches thick in ten years.
"Archaeologists," says Mr. Darwin, "are probably not aware how much they owe to worms for the preservation of many ancient Objects. Coins, gold ornaments, stone implements, etc., 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." The remains of ancient buildings seem also to have been buried effectively, in large part, through the action of worms. An example of this kind is furnished at Abinger, Surrey, where the remains of an ancient Roman villa were discovered in 1877. The cut (Fig. 6) represents the appearance presented by the buried wall and the ground around it at a point where one of the trenches was dug. The mold here was from eleven to sixteen inches thick over the tesselated floor, G, and from thirteen to fifteen inches thick over the broken summit of the wall, W. No signs of worms appeared on the trodden-down earth over the tesseræ when they were first cleared, but many signs of fresh worm-action were seen on the next day, and for the next seven weeks these signs were very abundant. Numerous burrows were also found in the course of the digging, and worms were brought up from a considerable depth. Three years afterward the worms were still at work, burrowing in the concrete floor and the mortar of the walls, as they had probably been doing ever since
|Mould, 9 inches thick.|
|Mass of rubbish 27 Inches thick, overlying a pile of charred wood.|
|Tesseræ, resting on concrete.|
|Fig. 7.—Section within a Room in the Basilica at Silchester. Scale 18|
the concrete had become decayed enough to allow them to penetrate it; and even before that period they probably lived under the floor, making burrows which, collapsing from time to time, helped make the walls and floor sink.