PART I. 



CHAPTER I. 



SCIENCES AUXILIARY TO GEOLOGY. 



Definition.— Physical Properties : Extension, Gravity, Impen- 

 etrability, Divisibility, Porosity, Indestructibility, Inertia. 



Geology is that branch of physical science which 

 treats of the constitution of the earth we inhabit. 

 It not only has for its objects an investigation into 

 the form and external characters of our globe, but 

 .also into the nature and relative position of the ma- 

 terials which constitute its external crust, and the 

 manner and order in which these materials have as- 

 sumed their present position. Geology, therefore, 

 embraces the science of Physical Geography ; but, 

 before entering upon this branch of our subject, it 

 will be proper to take a brief survey of those auxilia- 

 ry sciences, some acquaintance with which is indis- 

 pensable to a full understanding of what is to follow. 



The properties of material substances are of two 

 kinds, physical and chemical ; the study of the for- 

 mer comes under that department of science called 

 Natural Philosophy, the latter under that of Chemis- 

 try. 



The physical properties are either general or sec- 

 ondary ; those are called general which are com- 

 mon to all bodies, while the secondary only belong 

 to a few. Among the first may be enumerated Ex- 

 tension, Gravity, Impenetrability, Divisibility, Mobility, 

 Porosizy, Indestructibility, and Inertia, 

 B 



