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Show 168 WEIGHT OF EARTH CnAP. III. enclosed 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. Tho spot selected appeared neither particularly favourable nor the reverse for worms ; but I havo often noticed that castings are especially abundant on common land, and this may, perhaps, be attributed to the poorness of tho soil. The vegetable mould was here between throe and four inches in thickness. As this spot was at some distance from the house where the lady lived, the ca tings 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 wore 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., 3G7 CnAP. III. BROUGHT UP BY WORMS. 169 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, 1o·l tons of annually ejected dry earth. Suli1MARY OF TilE FOUR 1rourr.oorNG CASES. (t.) Castings ejected ncar icc wit.hin about a year, collcctccl by Dr. King on a square foot of surface, calculated to yield per acre 14. ·58 tons. (2.) Castings ejected dming about 45 days on a square yard, in a ficlcl or poor pasture at tho bottom of a I arge valley in the Chalk, calculated to yield annually per acre 18 ·12 t.ons. (3.) Castings collcctet1 from a square yard on an olcl terrace at Leith llill L lace, during 369 clays, calculated to yield annually per acre 7 ·56 tons. (4..) Castings collected from a square yard on Lcit.h Hill Common during 3G7 days, calculated to yiclJ annually per aero lG ·1 tons. Tlte tlticlcness of tlte layer of mould, whiclt castings eJected during a year would form if unijor1nly 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 |
