THE 



WONDERS OF GEOLOGY. 



INTRODUCTION TO THE AMERICAN EDITION, 



BY 

 PROFESSOR SILLIMAN. 



1. Object of the Science. — Geology is the natural history of 

 the earth ; its hills and mountains, its rivers, lakes, seas, and oceans, 

 its fertile plains and sterile deserts — in a word, all that belongs to 

 physical geography, is comprised in this science. Incidentally, it 

 takes notice of agriculture and commerce, of the various improve- 

 ments of civilization, and of the races and families of animated 

 beings of both organic kingdoms, since they are all influenced, 

 more or less, by geological phenomena. Every thing upon the 

 globe is, therefore, connected with geology, which embraces like- 

 wise the principal physical facts and events of which our planet has 

 been the theatre. 



But the more immediate object of this science is to ascertain 

 the structure of the earth, and the nature of the masses of which 

 its crust is composed — the order of their arrangement — their 

 mineral and organic contents — the proximate causes by which they 

 were formed and deposited, and those by which they are rendered 

 liable to future changes. 



2. Preliminary knowledge. — These considerations necessarily 

 involve a knowledge of physical laws. We must be acquainted 

 with the chemical constitution of matter, with the combinations its 

 elements are capable of forming, with the liabilities of the com- 



