"MANUAL OF GEOLOGY" 



account of the fuller knowledge of the facts finally at- 

 tained. In the development of the American continent 

 there are recognized, not only long periods of sedimenta- 

 tion and accumulation of strata in synclinoria, but separat- 

 ing these periods of quiet there were revolutions resulting 

 in each case in lifting greater or smaller areas permanently 

 above the surface of the ocean, and the later of these 

 revolutions were the grander, in amount of elevations and 

 mountain making, in fracturing and lava outflows, and in 

 production of volcanoes, because, as his theory explains, 

 of the greater thickness and rigidity of the crustal portion 

 of the earth incident to the secular cooling of the globe. 

 " Not only did Dana take this broad and comprehen- 

 sive view of the whole system of geological phenomena, 

 but he made a thorough and particular study of several of 

 the more difficult problems of American geology; among 

 them may be named the interpretation of the glacial 

 phenomena over New England and the classification of 

 the period for North America, the solution of the 

 ' Taconic ' controversy, and the associated questions of 

 metamorphism and mountain building." 



207 



