LIFE OF JAMES DWIGHT DANA 



ANALYSIS OF THE " MANUAL" BY PROFESSOR 

 H. S. WILLIAMS 



A fuller analysis of the Manual of Geology was prepared 

 by Prof. H. S. Williams, the present incumbent of the 

 Silliman Professorship of Geology in Yale University, 

 and a part of his analysis will here be quoted. The 

 entire paper may be found in the Journal of Geology, 

 Chicago, 1895, vol. iii., p. 6. 



" Geology is a much more complex and miscellaneous 

 science than either mineralogy or zoology, and therefore 

 it is difficult to so arrange the facts as to exhibit their re- 

 lation to any single common principle. But we believe 

 Dana's Manual has come nearer to the setting forth of 

 such an ideal system of geology than has been elsewhere 

 attained. The central ideas in this system are : (a) the 

 earth a cooling globe ; (b) contracting as it cools ; (c) differ- 

 ences of depression and elevation of the surface the direct 

 result of the unequal contracting; (d) oceans and con- 

 tinents permanent; (e) trends of shores, of islands and 

 mountains, according to system, and expressive of lines 

 of weakness, and of chief foldings and fractures; (/) 

 epeirogenic and orogenic phenomena the direct results of 

 the contracting; (g) climates and currents of the ocean 

 also the effects of changes in elevation of the continents ; 

 (ti) the separation of the history of the earth into ages by 

 the revolutions at the climaxes in the contraction, when 

 strain and tension came to exceed strength and resistance, 

 and resulted in folding and faulting and local disturbances, 

 and were marked by the greater or less extermination of 

 life, followed by repeopling by, and the modification of 

 the successors ; (i) the surface shaping of the continents 

 by ice and water action also influenced by oscillation of 

 level of the continents ; and all of these various factors 

 taking a part in producing the present complex condition 

 of the earth's surface. 



4 The earth as a whole was the unit which was before 

 his mind as he constructed this system of geology. As 

 he traced its history he saw in the successive events of 

 geology the marks of the gradual development of a 

 vaporous, then incandescent, and finally hardened, con- 



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