PRESENCE OF PHOSPHATE OF LIME. 309 



mineral, and for its subsequent manufacture into a port 

 able manure.* 



It is in favour of this^ expectation that Dr Henry 

 Rogers and others have observed, that crystallised blue 

 phosphate of iron is seen very plentifully as an incrusta 

 tion upon fossils and other substances in these green- 

 sand deposits a circumstance which indicates the actual 

 or former presence of phosphoric acid in considerable 

 quantity in the superior beds of rock, or in the waters 

 which trickle through them. 



The formation of the grains of green sand is a very 

 interesting subject of inquiry, both chemically and geo 

 logically. I cannot discuss the subject here. I may, 

 however, observe, that when examined under the micro 

 scope, these grains partake very much of a common 

 form round or oval, and kidney-shaped which has 

 induced Dr Henry Rogers to regard them as produced 

 by a natural deposition from hot solutions, containing 

 the several constituents of which the grains consist. 

 This ingenious explanation must be received with cau 

 tion, chiefly because of the difficulty of showing under 

 what circumstances solutions of such a kind, and in which 

 marine animals would live, could be produced and main 

 tained for so long a period over the large areas known 

 to be covered by the green-sand deposits. If we so far 

 modify the view as to allow the grains to have been 

 formed, as so many other mineral concretions have been, 

 in a semi-fluid mud spread over the bottom of a salt sea, 

 the objections which might be brought against it would, 

 I think, be less strong. 



* I am happy to say that the search has subsequently been rewarded 

 by the discoveiy of most valuable deposits of this mineral in the State 

 of New Jersey. By these I believe that English farmers are likely to 

 be first benefited, but, subsequently, I hope American farmers also will 

 be brought to use, for the renovation of those worn-out soils, the same 

 substances which the English farmer is willing to buy for the purpose 

 of keeping up the heart of his own. 



