43 



these alterations, he must needs be a prejudiced 

 and incompetent judge: they are necessarily left 

 to the experience of others, who will not fail to 

 improve that which is imperfect, and to reject 

 that which is incorrect. 



The reasons for the alterations that have been 

 made, are stated, wherever it appeared necessary, 

 in the different remarks which accompany the 

 work. Thus the student will be better enabled 

 to judge of their propriety ; and to distinguish 

 that which has received the writer's consideration, 

 from changes founded merely on caprice or the 

 love of novelty. 



The classification is simple ; all rocks being 

 referred to a primary and a secondary class, and 

 a smaller division being formed of those which 

 are found in both. The substances which cannot 

 be referred to the latter class, from their more re- 

 cent origin, are considered separately in an appen- 

 dix ; and a similar expedient is adopted for the 

 volcanic rocks. The reasons for this method of 

 division are given at more length in an appro- 



