Charles Davison — Work done hy Lobworms. 491 



from four areas on the Holy Island Sands with the following 

 results : — 



(1) About 100 yards from the Holy Island shore and nearly 

 opposite the village, a triangular area of 13,534 square inches was 

 measured off. It contained 87 castings, equivalent to 40,322 per 

 acre. Sixteen of these were collected ; their total weight when 

 dried was 7,955 grains, i.e. an average of 497 grains or about lyoz. 

 for each casting. Now, the number of high tides in the year is 705. 

 Hence, if the same number of castings are formed every day 

 throughout the year.' the total weight of castings thrown up 

 annually would be 901 tons per acre. 



(2) About 100 yards from the shore and nearlj'' opposite the 

 old lime-kilns, an area of 6,324 square inches contained 53 castings, 

 i.e. at the rate of 52 568 per acre. These castings were all large. 

 Six of them weighed 7,986 grains, or on an average 1,331 grains or 

 about 3 oz. each. The total weight thrown up annually would thus 

 be 3,146 tons per acre. 



(3) About 100 yards N.W. of the last place and the same distance 

 from the shore, an area of 7,844 square inches contained 88 castings, 

 equivalent to 70,372 per acre. AH of these castings were large. 

 Seven of them weighed 6,963 grains, i.e. an average of 995 grains 

 or about 2J oz. each. At this rate, the weight of sand brought up 

 annually would be 3,147 tons per acre. 



(4) About one mile N.W. of the village and a quarter of a mile 

 from the shore, an area of 5,304 square inches contained 38 castings, 

 or 44,941 per acre. These castings were very much smaller than 

 are usually found on the Holy Island Sands, and only about half the 

 average number per acre. Twenty ot" them weighed 4,444 grains, 

 i.e. an average of 222 grains or about half an ounce each ; giving a 

 total weight ejected annually of 449 tons per acre. 



Taking the average of these four estimates, we find that the 

 amount of sand brought up to the surface by lobworms every year is 

 1,911 tons per acre.^ But this is probably less than the actual 

 amount ; for, though the castings in the second and third areas were 

 larger than usual, yet in the fourth they were much below the 

 average size, and in every case the number of castings per acre was 

 less, and in two cases much less, than the average number formed on 

 the Holy Island Sands. 



On the north side of the island, in Caves Haven, castings were 

 collected from two places : 



(5) An area of 12,568 square inches contained 173 castings, 

 equivalent to 86,344 per acre. Sixty of these castings weighed 



^ I have not been able to learn anything decisive on this point, but I was informed 

 by a resident on Holy Island that the castings appeared to be quite as numerous there 

 in winter as in summer. 



3 Mr. Darwin has calculated the amount of soil brought up by earthworms in four 

 cases, one of these being near Nice and the other three in England. The results 

 are 14-58, 18-12, 7-56, and 16-1 tons per acre every year (pp. 160-)69). The 

 average ot these estimates being 14-09 tons per acre, it follows that the weight of 

 sand brought up by lobworms is 136 times the weight of soil brought up by earth- 

 worms over an equal area in the same time. 



