XIII. — hetter from Dr. Front to Dr. Bnckland respecting the Analysis 

 of the Fossil Fccces of Ichthyosaurus and other Animals. 



[Read April 3rd, 1829.] 



Dear Sir, 



1 HAVE examined the different specimens you were kind enough to send nie, 

 and found the composition of all of them to be very similar; that is to say, 

 they consist essentially of the phosphate of lime and carbonate of lime, 

 together with minute variable proportions of iron, sulphur, carbon, and occa- 

 sionally other matters. The relative proportions of the principal ingredients 

 appear to differ somewhat in the diBerent specimens, and even in different 

 parts of the same specimen; hence no formal analysis has been attempted; 

 but the phosphate of lime may perhaps be estimated to constitute from about 

 one-fourth to three-fourths of the whole mass. The iron and sulphur appear 

 to exist in some instances, partly as a sulphuret of iron, and partly in a state 

 of oxidation ; and the dark-coloured varieties, in which these principles exist 

 in greatest abundance, appear to owe their colour chiefly to these substances 

 and a little carbonaceous matter. 



The above composition seems to prove beyond a doubt the animal origin 

 of these bodies, or, in other words, that their basis is bone. The question is, 

 by what means bone can be made to assume the appearances presented by 

 them. That mere time, and the circumstances to which they have been 

 exposed, are not sufficient to account for these changes, seems to be proved 

 by the fact, that many of the specimens contain fragments of bone possessing- 

 its original characteristic structure. We must therefore seek for some other 

 explanation ; and your opinion that they are of feecal origin, or of the nature 

 of album graecum, seems to me to off"er a very satisfactory solution, and to 

 account at once for tlieir chemical composition, for their form, and for their me- 

 chanical structure, which can hardly be explained on any other supposition. 



Nor do 1 see any serious objection to your opinion, that these substances 

 are the mineralized fseces of carnivorous reptiles of the Saurian and analogous 

 tribes, the fossil remains of which exist so abundantly in the same strata. The 

 ])roper faeces of existing animals of this kind, consist principally of the phos- 

 phate of lime, and often assume the form of album grascum. These animals 

 also pass immense quantities of concrete urine, consisting* principally of the 



