PREFACE. 



THE first idea that suggested itself to me, in regard to a 

 work of this kind, was to publish a few plain instructions 

 for drawing geological boundary-lines, a practical matter 

 which seemed to have been somewhat neglected, although 

 it is of considerable importance. 



But there is an almost imperceptible transition from 

 mapping rocks, which appear at the surface of the earth, 

 to tracing those that are beneath, and from defining the 

 extent of a formation to the determination of its history, 

 as expressed in its lithological character and fossil re- 

 mains. 



The idea, therefore, while being realised, expanded 

 to much beyond its original dimensions, still there is 

 scarcely any portion of the book in which the matter 

 might not, with advantage, be enlarged. It has, how- 

 ever, been thought advisable to issue, as it is, this first 

 edition, and leave for a second (should it ever be re- 

 quired) any further extension. 



There are so many subjects of which a knowledge is 

 -an advantage in geological surveying, that it is difficult 



