2l6 GEOLOGY [CHAP. IX 



Letter 551 To J. H. Gilbert. 1 



Down, Jan. I2th, 1882. 



I have been much interested by your letter, for which I 

 thank you heartily. There was not the least cause for you 

 to apologise for not having written sooner, for I attributed 

 it to the right cause, i.e. your hands being full of work. 



Your statement about the quantity of nitrogen in the 

 collected castings is most curious, and much exceeds what I 

 should have expected. In lately reading one of your and 

 Mr. Lawes' great papers in the Philosophical Transactions^ 

 (the value and importance of which cannot, in my opinion, 

 be exaggerated) I was struck with the similarity of your 

 soil with that near here; and anything observed here would 

 apply to your land. Unfortunately I have never made deep 

 sections in this neighbourhood, so as to see how deep the 

 worms burrow, except in one spot, and here there had 

 been left on the surface of the chalk a little very fine ferru- 

 ginous sand, probably of Tertiary age ; into this the worms 

 had burrowed to a depth of 55 and 61 inches. I have never 

 seen here red castings on the surface, but it seems possible 

 (from what I have observed with reddish sand) that much of 

 the red colour of the underlying clay would be discharged in 

 passing through the intestinal canal. 



Worms usually work near the surface, but I have noticed 

 that at certain seasons pale-coloured earth is brought up from 

 beneath the overlying blackish mould on my lawn ; but from 

 what depth I cannot say. That some must be brought 

 up from a depth of four to five or six feet is certain, as the 

 worms retire to this depth during very dry and very cold 

 weather. As worms devour greedily raw flesh and dead 

 worms, they could devour dead larvae, eggs, etc., etc., in the 

 soil, and thus they might locally add to the amount of nitrogen 

 in the soil, though not of course if the whole country is con- 

 sidered. I saw in your paper something about the difference 



1 The late Sir J. Gilbert, of Rothamsted. 



2 The first Report on " Agricultural, Botanical, and Chemical 

 Results of Experiments on the Mixed Herbage of Permanent Grass- 

 land, conducted for many years in succession on the same land," was 

 published in the Philosophical Transactions of the Royal Society 'in 1880, 

 the second paper appeared in the Phil. Trans, for 1882, and the third 

 in the Phil. Trans, of 1900, Vol. 192, p. 139. 



