XI 1 PREFACE. 



those who have nothing left to learn, equally 

 redundant. 



in considering the different plans on which a 

 classification of rocks might be constructed, he 

 was, without hesitation, led to adopt one founded 

 on the geological relations and positions of rocks 

 in nature. The reasons for this choice are stated 

 at full length in an introductory chapter. It is, 

 however, necessary here to remark, that the basis 

 of the arrangement is virtually the same as that 

 adopted by Werner. But, in the execution, it 

 differs in many important particulars ; either in 

 consequence of the author's own observations, 

 or of the views which have been more recently 

 formed of the order of nature, by those geologists 

 who, uneducated in the principles and doctrines 

 of the German school, have undertaken to ob- 

 serve and think for themselves. 



However numerous the varieties of rocks may 

 appear to an inexperienced eye, and whatever 

 confusion and uncertainty may at first seem to 



