PHOSPHATES USED IN AGRICULTURE. 637 
itself, that their true colour is only seen when they are 
broken. They contain 60 to 65 per cent, of phosphate of 
lime, sometimes rather more, and, when ground, form a 
yellowish-white powder. They are supposed to be the fossil 
excrement of extinct animals, hence their curious name, de¬ 
rived from the Greek; but we have not sufficient proof of 
this extraordinary supposition. However, the revelations of 
geology during the past twenty years have been so exceed¬ 
ingly 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 correspond 
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. Thev alwavs contain a certain amount of red 
V * 
oxide of iron, and about 56 per cent, of phosphate of lime; 
they are consequently rather less valuable than the pure 
Cambridge coprolites; moreover, 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 
certain amount of carbonate of lime and insoluble silicious 
matter, and it is important to manufacturers and agricul¬ 
turists 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, &c. 
But the whole of the Upper Green Sand formation of 
England is characterised 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 
