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mulation as {)eat-bogs, etc., and, 2nfl, animal agencies, such as coral 

 reefs and other subjects of that nature. 



The third division, Historical geology, or as some call it "Stati- 

 graphical geology, ti'eats of the rocks in the order of their formation with 

 the contemporaneous events in their geological history, and includes 

 both stratigraphical and paleontological geology, the latter being 

 regarded by some, however, as a distinct branch, with a review of the 

 laws or systems of progress in the globe and in its kingdoms of life. 

 While in this place we can only consider the science of geology 

 properly so called, we may say that its relation to many other 

 physical sciences is exceedingly intimate. Among these may be 

 specially ni3ntioned astronomy, chemistry, mineralogy, zoology and 

 botany, with all of which, and with others, the elucidation of the 

 many geological problems which constantly arise requires an acquaint- 

 ance more or less profound. In the present stage of the science 

 each of these subjects is frequently assigned to a specialist in that 

 particular branch, in so far at least as it applies to the science of 

 geology. Thus the chemist and lithologist study the composition and 

 peculiarities of the several kinds of rock structure. The paleontologist 

 studies the remains of organic life, in which now paleontological botany 

 forms a special branch. The mineralogist works out the peculiar 

 properties of the several varieties of minerals wliich are encountered, 

 and this division of study is carried on almost indefinitely in certain 

 lines ; thus one person devotes his time to studying the peculiarities of 

 special forms of life, as, for instance, the graptolites, the trilubites, the 

 extinct mummalia, and so on. 



With the early history of our planet, or that part of its history 

 which jjrecedes the appearance of solid land, known in geological 

 language as the Laurentian time, geology proper is supposed to have 

 nothing to do, its strict province being confined to the study of the rocks 

 of the earth's crust itself. So intimately, however, are the rocks of the 

 Laurentian time connected with the original crust of the earth that the 

 consideration of the agencies which led to the deposition or formation 

 of tluit crust is by many regarded as strictly within the province of 

 geological investigation, and in most works on the science we find a 

 chapter devoted to the early history of the earth, viz. : that portion of it 



