52 



might present no differences of character ; and, 

 perhaps, sometimes cause us to lose sight of an 

 important circumstance of analogy in geological 

 science. 



In considering the numerous substances ar- 

 ranged in the following catalogues, it will be ap- 

 parent that there is a considerable deficiency of 

 terms by which to distinguish them. In this re- 

 spect, the history of rocks has not kept pace with 

 that of the simple minerals ; in which, new names 

 have been adopted as fast as the discovery of a 

 new species or variety rendered one necessary : 

 much faster, it might indeed be added. This dif- 

 ference in the progress of the two catalogues has 

 perhaps been unavoidable. The names of rocks 

 having been rather of popular than scientific ori- 

 gin, no great attention was paid towards the dis- 

 crimination of the substances which entered into 

 their composition, the various modes in which 

 these were combined, or the different circum- 

 stances of structure which might have afforded 

 justifiable grounds for distinctions. In the mean 

 time, the science of geology has been rapidly ad- 



