PREFACE. XI 



a new classification of rocks would have been the 

 result ; as it was impossible to introduce all the 

 requisite illustrations, and as some of the rocks 

 found in nature do not exist in those islands. 

 It seemed therefore preferable to reserve this 

 matter for a separate essay ; a work which seemed 

 to be imperiously called for by the want of any 

 similar system to which a student could refer for 

 information. 



A more minute attention to the subject, and 

 a recollection of the difficulties which the author 

 himself had experienced in the commencement of 

 his pursuits, when he had nothing to consult but 

 the great book of Nature, led to many modifica- 

 tions, not only of the original design, but of 

 the whole execution. If, in attempting to render, 

 not only himself, but the subject which he has 

 undertaken, thoroughly intelligible to those who 

 have every thing to acquire, he has been led into 

 a degree of minuteness which the accomplished 

 geologist may disdain, he has been guided by a 

 recollection of the gratitude which he would once 

 have felt for information equally minute, and, to 



