"MANUAL OF GEOLOGY" 



as it has been recognized, is simply this : Unity evolving 

 multiplicity of parts through successive individualizations 

 proceeding from the more fundamental onward ' (p. 346). 



" Notwithstanding all the additions of details and 

 statistics in illustration and elaboration of this idea, we 

 see, up to the last, this is the dominating principle about 

 which his system of geology was built ; and the American 

 continent, as its geological features were gradually opened 

 to light, was recognized as the most typical illustration of 

 this system to be found upon the globe. In the last 

 edition of the Manual we find these words: ' North 

 American geology is still its chief subject. . . . The 

 idea long before recognized (i. e., before 1855) that all 

 observations on the rocks, however local, bore directly on 

 the stages in the growth of the continent, derives univer- 

 sal importance from the recognition of North America as 

 the world's type-continent the only continent that gives, 

 in a full and simple way, the fundamental principles of 

 continental development.' 



" He was not, however, carried away by theories; his 

 scientific research was always deep, thorough, and exact. 

 As he was preparing the report on the geology of the 

 Exploring Expedition he was not satisfied with simply 

 describing what he saw. He not only made a thorough 

 study of the volcanoes in the islands of the Pacific and 

 on the borders of the South American continent, and 

 Vesuvius and ^Etna in Italy [his first scientific paper, as 

 before noticed, was a letter written from the U. S. ship 

 United States, in 1834, " On the Condition of Vesuvius in 

 July, 1834 "], but in his investigations of the many ques- 

 tions raised by these observations he also studied the sur- 

 face of the moon, and comparison of the already cooled 

 moon and its extinct craters with the present condition 

 of the earth suggested the chief phenomena about which 

 was later elaborated his theory of the earth's develop- 

 ment as a cooling and necessarily contracting globe. 



The general contraction theory was not original with 

 Dana, as he acknowledged in these papers. He found it 

 advocated by Leibnitz in 1691. Babbage and De la 

 Beche had formulated the general theory of changes of 

 level by contraction and expansion and the rise of con- 

 tinents. Mather, Elie de Beaumont, Lyell, and others 

 had made more or less reference to the principle, and M. 



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