THE 



ANCIENT LIFE-HISTORY 



OF 



THE EARTH, 



INTRODUCTION. 

 THE LAWS OF GEOLOGICAL ACTION. 



UNDER the general title of " Geology " are usually included at 

 least two distinct branches of inquiry, allied to one another in 

 the closest manner, and yet so distinct as to be largely capable 

 of separate study. Geology,* in its strict sense, is the science 

 which is concerned with the investigation of the materials which 

 compose the earth, the methods in which those materials have 

 been arranged, and the causes and modes of origin of these 

 arrangements. In this limited aspect, Geology is nothing more 

 than the Physical Geography of the past, just as Physical Geo- 

 graphy is the Geology of to-day; and though it has to call in 

 the aid of Physics, Astronomy, Mineralogy, Chemistry, and 

 other allies more remote, it is in itself a perfectly distinct and 

 individual study. One has, however, only to cross the thresh- 

 old of Geology to discover that the field and scope of the 

 science cannot be thus rigidly limited to purely physical pro- 

 blems. The study of the physical development of the earth 

 throughout past ages brings us at once in contact with the 

 forms of animal and vegetable life which peopled its surface in 

 bygone epochs, and it is found impossible adequately to com- 

 * Gr. ge, the earth ; logos, a discourse. 



