The Phosphates used in Agriculture. 277 



sufficient proof of this extraordinary supposition. However, 

 the revelations of geology during the past twenty years have 

 been so exceedingly wonderful, that one is readily tempted to 

 admit that some of these coprolites are the fossil excrement of 

 certain extinct animals, probably reptiles, and therefore cor- 

 respond somewhat in their chemical composition to guano 

 which has been deprived of its organic matter by atmospheric 

 influences. Specimens of such guano have given me, upon 

 analysis, from 15 to 30 per cent, of carbonate of lime, which 

 resembles the proportion of carbonate of lime invariably present 

 in every description of coprolites. 



The main thing that regards the agriculturist or manure 

 manufacturer, however, is their chemical composition, by which 

 these Cambridge coprolites appear to be the cheapest source of 

 phosphate of lime at present known. The Suffolk coprolites 

 are dark brown nodules, some of which have very much the 

 appearance of fossil bones rounded by the action of the sea. 

 They always contain a certain amount of red oxide of iron, and 

 about 56 per cent, of phosphate of lime ; they are consequently 

 rather less valuable than the pure Cambridge coprolites ; more- 

 over, they appear to belong to the tertiary formations. 



All these coprolites, and, indeed, all natural phosphates 

 used in agriculture, except apatite (see further), contain a cer- 

 tain amount of carbonate of lime and insoluble silicious matter, 

 and it is important to manufacturers and agriculturists to have 

 the proportions of these determined accurately, otherwise they 

 have no control over adulteration, and no basis to work upon in 

 the manufacture of artificial manures. 



Along with Cambridge coprolites I have found fragments 

 of fossil bone — bones of reptiles, probably — showing the same 

 chemical composition as the rounded nodules or coprolites 

 themselves. The Suffolk coprolites appear to be chiefly fossil 

 bone, more or less impregnated with phosphate of iron, etc. 



But the whole of the Upper Green Sand formation of Eng- 

 land is characterized by a wide diffusion of phosphoric acid in 

 the shape of phosphate of lime. My attention was called to 

 this some years ago, by a relation who forwarded to me a very 

 large specimen of fossil wood from the Green Sand of the Isle 

 of Wight, which, upon being submitted to analysis, gave me an 

 enormous proportion of phosphate of lime — in fact, it was 

 chiefly formed of this substance and fluorspar — though it was 

 not apatite ;* and I learnt afterwards that Mr. Thomas Way 

 had formerly examined several fossil polyps, sponges, etc., 

 from the Green Sand, which gave a very large per-ccntage of 

 phosphate of lime. 



* See Report of British Association, 1861, and Chemical Newt, 1861. 



