CHAPTER I 



THE SUCCESSION OF STRATIFIED K< > 



Scope of the Subject. In some manuals of Geology thi* 

 branch of the subject is called Stratigraphical Geology, because it 

 chiefly consists in the description of the great stratified series of 

 rocks which make up the mass of the earth's mi>t . It is some- 

 tinifs called historical geology because it should comprise not only 

 a description of the various rocks which were formed during each 

 period of the world's history, but also some description of the 

 fossils found in each formation, and some account of the physical 

 conditions under which the rocks themselves were deposited, with 

 a notice of the changes in the relative position of land and sea 

 which took place from time to time ; all this should be made 

 as complete as the imperfection of the geological documents will 

 allow. 



In brief, historical geology should gather up the knowledge 

 acquired in all the other departments of the science, and should 

 apply it to the elucidation of the history of the earth, or of a 

 portion of the earth, from the earliest time of which any record.* 

 exist down to the time of human history. 



At present there are only a few limited areas of the earth's 

 surface about which we have anything like a full stratigraphical 

 knowledge, and much remains to be learnt even in the areas about 

 which we know most. Historical geology, therefore, is yet in it* 

 infancy ; but enough is now known of the stratigraphical geology 

 of Europe to make it possible to give an outline of its geological 

 history, and American geologists an- rapidly making it possible to 

 do the same for North America. 



The Succession of Stratified Rocks. The general 

 principles on which stratigraphical geology is founded are easily 

 understood, and the manner in which tin- unlrr and succession of 

 rock-groups is established will now be hii. ll\ explained. The 

 mere succession of strata in any district <>i country, lu.wuver, i> 



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