THE SECONDARY STRATA. 263 



as in the preceding and connected lias ; the whole 

 produced in one period of a populous repose, if under 

 a gradually increasing population. 



It ceases with the green sand: and here, I fear, geo- 

 logical philosophy is scarcely less at a loss than in the 

 previous case of the red marl ; while, in reality, the 

 particular difficulty, surmountable there, seems here 

 to be absolutely insuperable. The degradation of the 

 land goes on, but the deposits of limestone diminish 

 or stop. Sand is deposited, and so is clay ; but ani- 

 mals do not breed, or breed scantily, among these 

 deposits. There is no mark of revolution or tumult, 

 the strata are orderly and consistent, and continue 

 to be parallel ; yet the organic creation, if it has not 

 disappeared, has been so reduced, that it bears no 

 longer any proportion in quantity to the time required 

 for this deposit. It is not exterminated, because the 

 green sand does contain limestone, marls, and shells ; 

 as it also contains lignites and vegetables, the former, 

 in some places, conspicuously. 



I can give no solution of this diminution of animals, 

 and through so long a period ; I cannot even offer a 

 conjecture respecting what geologists have forgotten 

 to notice, from never bestowing the needful reasonings 

 on the facts before them. Some change in the con- 

 stitution of the earth, or the water of the earth at least, 

 must have occurred ; while, of this, there are no other 

 indications. Must we suppose that something has 

 been overlooked respecting this deposit and the inter- 

 val which divides it from the oolithe series? This is 

 what geology has still to investigate ; and till it has so 

 done, and furnished facts for the explanation of this 

 change, it has left an essential portion of its work un- 

 thought of. My own opportunities as to this interval 

 have been few ; and when I seek among writers, I find 

 nothing to the purpose. 



