AND ANALOGIES, OF ROCKS. 233 



intermixture, occasional transitions may also happen 

 between coarse argillaceous schist and quartz rock, 

 or between the fine schist and gneiss. But these are 

 rare and easily explained ; nor is there any transition 

 from limestone to any other rock. In the newer 

 strata, it is equally easy to understand how they must 

 happen, from the irregular succession of so small a 

 number of materials, and how some uncertainty of 

 composition must often take place at the point of 

 change between different deposits. This subject is 

 however noticed more particularly in the chapter on 

 the Successions of Strata ; and the particular transi- 

 tions will be pointed out, where necessary, in the 

 histories of individual rocks hereafter. It is to be 

 feared that the imaginary value attached to these 

 transitions, has arisen from the practice, far too 

 general, of deducing conclusions respecting the order 

 of nature, from that made by a mineralogist in his 

 cabinet. Undoubtedly, a rich cabinet may be made to 

 produce every transition which the most arduous 

 theorist could devise ; but he will have far mistaken 

 the real objects of his geological pursuits, who shall 

 make his drawer the type of Nature. 



