254< On the Chcmkal Composition of Clay-slate. 



in determining whether they had belonged to saurian animals 

 or to fishes, as I at one time, founding on the usual views of 

 chemists respecting the nature of recent saurian scales, had 

 thought might have been the case. 



In the second place, it may be a matter of inquiry, which is 

 left to any one who may be inclined to follow out the subject, 

 what differences existed between the dermal covering of extinct 

 saurian animals, and that of existing species of this description ; 

 for if there is any foundation for the view that the flat scales of 

 recent crocodilean animals consist of horny or other highly 

 azotized matter, and contain little or no bone-earth, then it is clear 

 that they differ from those at least of some extinct animals of 

 this nature. 



The very limited number of undoubted fossil saurian scales 

 which I have had an opportunity of seeing, or of which I have 

 read particular descriptions, agree in the above-mentioned exter- 

 nal character of having their surface hollowed into hemispherical 

 cavities of considerable size, in proportion to the magnitude of 

 the scale. This observation applies to the Caen scales ; to those 

 of the crocodile of Argenton, which I have never seen, but 

 which are described by Cuvier in the Ossemens Fossiles ; and 

 to those of the Monheim Gavial of Soemmering, in the British 

 Museum. This character I have also observed in the carinated 

 dorsal and bony-looking scales of some large recent crocodiles; but 

 whether it would afford a means of distinguishing fossil saurian 

 from fossil fish scales, is a point which I do not pretend to de- 

 cide, and leave to others who have more ample information, and 

 opportunities of observation on the subject. 



On the Chemical Composition nf Clay-Slate. By IIekmaxn 

 Fkick.* 



The chemical composition of clay-slate has hitherto been but 

 little examined, and the investigations that have been made 

 have yielded very different results. The following table con- 

 tains all the analyses with which I am acquainted, viz. : 



• Tom. V. part ii. p. 1G8. 

 From Poggendorf's Annalen, 1835. 



