70 



mariner of superposition, or interference, or -both. 

 And there is in fact, ample evidence that, in many 

 cases, the unstratified secondary rocks are thus 

 connected with the primary strata: the proof of 

 their true nature being founded on community of 

 mineral structure between these masses and 

 others of more extensive connexions, on prox- 

 imity of position, and on other concurring cir- 

 cumstances. 



In other cases, however, there is not the same 

 evidence; and there is then less facility in deter- 

 mining whether such unstratified rocks are of a 

 secondary origin, or whether they may not have 



been formed previously to the deposition of the 





 secondary strata, The classification therefore 



here fails to possess all the requisite evidence of 

 a natural arrangement : it is to be seen whether 

 it does not probably still remain natural, and 

 whether it is not practically convenient. 



In the first class, there is one decided division 

 of unstratified substances^ namely, granite, of a 

 peculiar mineral character, and always inferior to 

 the stratified rocks ; its nature, and the proof of 

 its position being unequivocal* The characters of 



