CHAPTER I. 



GENERAL GEOLOGICAL FACTS AND PRINCIPLES. 



1.01.01.* In the advance of geological science the standpoints 

 from which the strata forming the earth's crust are regarded neces- 

 sarily change, and new points of view are established. In the last 

 two years two have become especially prominent, and there are 

 now two sharply contrasted positions from which to obtain a con- 

 ception of the structure and development of the globe. The first 

 is the physical, the second the biological. We may, for example, 

 consider the surface of the earth as formed by rocks, differing in 

 one part and another, and these different rocks or groups of rocks 

 are known by different names. The names have no special refer- 

 ence to the animal remains found in them, but merely indicate that 

 series of related strata form the surface in particular regions. On 

 the other hand, the rocks are also regarded as having been formed 

 in historical sequence, and as containing the remains of organisms 

 characteristic of the period of their formation. They illustrate the 

 development of animal and vegetable life, and in this way afford 

 materials for historical-biological study. In the original classifica- 

 tion the biological and historical considerations are all-important. 

 But when once the rocks are placed in their true position in the 

 scale, and are named, these considerations, for many purposes, no 

 longer concern us. The formations are regarded simply as mem- 

 bers in the physical constitution of the outer crust. The Interna- 

 tional Geological Congress held in Berlin in 1885 expressed these 

 different points of view in two parallel and equivalent series of 

 geological terms, which are tabulated on p. 4. They are now very 



* The numbers at the beginning of the paragraphs are so arranged 

 that the first figure denotes the part of the book, the next two figures 

 the chapter, and the last two the paragraph. Thus 1.06.21 means Part 

 I., Chapter VI., Paragraph 21 under Chapter VI. 



