492 Charles Davison — Work done by Lobworms. 



6,119 grains; or, on an average, 102 grains or about a quarter of 

 an ounce each. At this rate the total weight of sand brought up 

 annually would be 396 tons per acre. 



(6) An area of 13,154: square inches contained 158 castings, 

 equivalent to 75,345 per acre. Sixty of them weighed 6,835 grains, 

 i.e. an average of 97 grains or less than a quarter of an ounce for 

 each casting. The total weight of sand brought up annually would 

 thus amount to 329 tons per acre. 



The average of these two estimates is 363 tons per acre, less than 

 one-fifth of the average for the Holy Island Sands. But it must 

 be much less than the amount of sand actually brought up, for the 

 castings in Caves Haven had evidently suffered considerable degra- 

 dation and some may have entirely disappeared. 



Volume of sand spread over a given area. — After the sand from 

 each of the six areas had been thoroughly dried and weighed, it was 

 placed in a measuring-glass and pressed firmly down, in order to 

 determine roughly the volume of sand brought up annually over an. 

 acre. The results are given in the following table : — 



On the Holy Island Sands, therefore, the average volume of sand 

 ejected by lobworms every year is 47,237 c. ft. per acre, and the 

 average thickness of the layer formed by it is 13 inches. In Caves 

 Haven, the average volume of sand ejected annually is 8,931 c. ft. 

 per acre, and the average thickness of the layer formed by it is 2^ 

 inches. 



Now, according to Carpenter, the depth to which lobworms 

 burrow is from 12 to 18 inches, and according to Johnston about 

 two feet.i Taking the higher of these two estimates, it follows that, 

 in the Holy Island Sands, the layer of sand in which the lobworms 

 live must on an average pass through their bodies once in 22 months. 



Geological wo)k of Lobworms. — The figures above given will show, 

 I think, how important is the work accomplished by lobworms. 

 We have seen that over an acre nearly two thousand tons of sand 

 are brought up by them in the course of a year and deposited on the 

 surface. Of course, the distance through which it is carried is not 

 great; but, unlike most other agents of geological change, it is 

 carried in the direction opposite to that in which gravity acts. The 

 uppermost layer of sand must frequently pass through the bodies of 

 lobworms, and in this way the sand-particles must become slightly 



1 Dr. W. B. Carpenter, "Zoology" (1867), vol. ii. p. 300. Dr. G. Johnston, 

 " A Catalogue of the British Non-parasitical Worms in the Collection of the British 

 Museum " (1865), p. 230. 



