Shaler.] 232 [March 2, 



beds as the result of the decay of vertebrate remains, the general 

 character of the deposit soon compelled me to seek some other ex- 

 planation of its origin. 



It has been suggested by a distinguished chemist that the deposit 

 was the result of the submergence of a great guano area, during 

 which submergence the bones of marine animals became mingled 

 with the mass. There are several objections to this view: in the first 

 place, no remains of birds have been found in the deposit, though 

 fossils quite as likely to be destroyed, are well preserved there. Then 

 it is difficult to see how in the immediate past this swampy shore 

 could have been the breeding place of the quantities of birds which 

 would have been required to have accumulated these phosphates, nor 

 could we suppose that the climate of this shore could have been at 

 the time of the deposition of the phosphates so different from what it 

 is at present, as would have been required to produce the dry condi- 

 tions essential to the accumulation of a guano deposit. 



There is another view of the origin of these phosphate beds, which, 

 so far as my knowledge goes, has not yet been suggested, and which, 

 it seems to me, solves a part of the difficulties. 



The phosphate layer rests upon a mass of marl containing a num- 

 ber of fossils which are found in a worn condition mingled with the 

 phosphate nodules. The analyses of Dr. St. Julien Ravenel have 

 shown that at several points beneath the phosphate beds the marl 

 contains several per cent, of phosphate of lime, and it may be as- 

 sumed as eminently probable that the whole of the marl beneath the 

 region where the phosphate beds occur, contains a certain quantity 

 of this material, mingled with the carbonate of lime which constitutes 

 the mass. Now it is a well known fact that water containing car- 

 bonic acid gas in solution has a solvent action upon both these salts 

 of lime, but that its power is greatest on the carbonate of lime. So 

 that a mass of marl containing both these materials, submitted to the 

 action of water charged with carbonic acid, might have the carbonate 

 of lime entirely removed, and the mass left behind when the solving 

 action ceased, might consist almost altogether of the phosphate of 

 lime. 



If we look a moment at the conditions which prevail in the phos- 

 phate region, we shall see that with this view we can easily frame 

 an explanation of the formation of this phosphate layer. The usual 

 section through these beds gives us on top a layer of vegetable matter 



