LIFE OF JAMES DWIGHT DANA 



Constant Provost had published in 1860 his view that the 

 agency of contraction alone will account for the various 

 changes of level which the continental areas have under- 

 gone. There were, however, certain features which were 

 his own, as shown in the following passage: 



' The reader will perceive that although the main 

 principles of Provost are sustained by the writer in this 

 and his former paper, the manner in which these prin- 

 ciples are carried out, is in some respects a little different, 

 especially in the idea that the oceanic areas have been 

 the more igneous parts of the globe, and for this reason 

 have contracted most; that certain orographic changes 

 over the continents are due to contraction beneath the 

 oceanic regions, and that the fissurings and mountain 

 elevations have for this reason taken place in some in- 

 stances near the margin of a continent, or near the limit 

 between the great contracting and non-contracting (com- 

 paratively non-contracting) areas. The efficiency of the 

 cause of contraction has appeared to the writer to be 

 wider and more evident, as the subject has received closer 

 attention; and the study of it very naturally led to 

 modification of former views.' * 



' Thus, it will be seen that, although others had before 

 conceived of the idea of the general effects of contraction, 

 it was to Dana the working hypothesis in the construction 

 of a system of geology. 



" Although later investigations have added new light 

 for the interpretation of the details of mountain building 

 and earth shaping, a reference to the chief points of the 

 theory, as elaborated by Dana in 1847, w ^l show how 

 much we are indebted to him for a clear exposition of the 

 general principles of the science. . . . 



' While Dana was a consistent uniformitarian, in so far 

 as to interpret past phenomena of the earth's history by 

 the operations of forces such as are now in action, he 

 clearly saw the natural relations of periods of special dis- 

 turbance of the strata by the reaching of high degrees of 

 tension and their expression in elevation and fractures 

 along lines of tension, and the more quiet periods of chief 

 sedimentation. This principle is better elaborated in the 

 latest edition of the Manual than in previous works, on 



* American Journal of Science, Series II., vol. iii., p. 179, 1847, 



2O6 



