238 Dr. Prout on the Ana{i/sis of the Fossil Fccces of Ichthi/osaurus. 



lifhate of ammonia; but, as this latter is comparatively a destructible sub- 

 stance, it could hardly be expected to be met with in the present instance 

 under circumstances so unfavoura1)le for its preservation*. 



The lithic acid, however, is one of the most permanent of animal subf-tances, 

 as is shown by the great length of time that urinary calculi composed of it 

 may be preserved ; but more esj)ecial!y by the fact that it exists unchanged in 

 llie substance called guano, after exposure to the atmosphere, &c. for ages. 

 Hence, perhaps, it is not too much to expect, that under favourable circum- 

 stances this principle also may hereafter be found of antediluvian origin. 



Sackville-street, I remain, dear Sir, 



March 14, 1829. Yours very truly. 



The Rev. Dr. Buckland. William Puout. 



* I first published many years ago an account of the composition of the urinary excrements of 

 the Boa constrictor (see Annals of Philosophy, vol. v. p. 41 3.) ; since which lime I have examined 

 those of the crocodile and other reptiles, and found them exactly similar. As my attention at 

 that lime was not directed to the faeces, though I noticed their composition, I did not publisli an 

 account of them ; but the late Dr. Marcct, to whom I presented specimens of both kinds of ex- 

 crement, has given an account of their composition. Of the faeces he says, " This substance I 

 did not (ind to contain any lithic acid, but it corisisted chicjly of the phosphate of lime., and 

 appeared to be nothing but the undigested residue of the food of the animal." — Essajj on Cal- 

 culous Disorders, p. 140, First Edition. 



