TJHI7EHSIT7 



PHYSICAL GEOLOGY. 



CHAPTEK I. 



DEFINITION AND ORIGIN OF THE SCIENCE. 



Objects and Scope of Geology. The term " science " is understood 

 to express, not only the information or facts collected, and the laws 

 founded on this knowledge, but also the ultimate objects and whole 

 field of research. Thus the science of Geology embraces that depart- 

 ment of the philosophy of nature, which investigates the formation 

 and structure of the earth and its system of development, including the 

 building up of rocks, succession of life, production of minerals, &c., 

 and all the changes which the earth has undergone. Geology, in fact, 

 treats of the earth's history and its constitution as a planet, subject to 

 physical laws that have produced changes in the materials of the earth's 

 crust, and have modified the succession and distribution of life in 

 different regions from age to age. 



It is in conformity with this ordinary language that we shall 

 endeavour to define geology. None of the sciences of observation has 

 made more remarkable progress toward successful generalisation than 

 this, yet the prospect of further discovery is so much richer than the 

 retrospect, and the ability employed in the research is so much more 

 skilled now, that we can hardly offer too expanded an expression for 

 the ultimate aims of geology. 



Geology then, in its fullest extent, is that science which undertakes 

 to investigate the ancient natural history of the earth ; to determine 

 by observation what phenomena of living beings or inorganic matter 

 were formerly manifested on or within the globe, in what order and 

 under what conditions ; to employ the comparative data, which are 

 furnished by investigating the present operations of nature as a means 

 for characterising and measuring the successive revolutions which the 

 earth has undergone before it arrived at its present state ; and thus, 

 finally, to furnish a complete historical view of the conditions which 

 have regulated, and still regulate, its system of mechanical, physical, 

 chemical, and vital phenomena. 



From the terms of this definition we may at once understand why, 

 VOL. i. A 



