PART II, 



GEOLOGY. 



CHAPTER I. 



GEOLOGY investigates the nature, composition, origin, struc- 

 ture, and arrangement of the materials of which the earth 

 is composed. Geology may be divided into three parts, viz: 

 1. Chemical Geology, which investigates the chemical nature 

 and composition of the various materials of which the earth 

 is made up. 2. Mechanical Geology, which treats of the 

 arrangement, structure and relative position of these various 

 materials. 3. Historical Geology, which treats of then: relative 

 ages and origin, and the changes which they are undergoing.* 



Every part of the earth, including air and water, except 

 undecomposed animal or vegetable matters, is regarded as 

 mineral. 



The term rock, in geological language, includes besides the 

 solid parts of the globe, the loose materials, such as sand, 



* This division is proposed by the author, and is, like all the othe rs 

 which have been proposed, imperfect, and, in some respects, objec- 

 tionable. It has the advantage of being plain and convenient: such a 

 division, however, whether perfect or imperfect, is not indispensable to 

 the successful study of Geology. 



