JAMES DWIGHT DANA 263 



geneous mantle of clay, gravel, and boulders, covering much of 

 the area of Canada and the northeastern United States, as well as 

 northwestern Europe, and commonly called "drift." In opposi- 

 tion to the older diluvial theories, Agassiz had advocated the doc- 

 trine that the drift was due to the action of a glacier of continental 

 extent. Dana clearly indicated his sympathy with the views of 

 Agassiz in his presidential address before the American Association 

 for the Advancement of Science in 1855, and in the Manual in 

 1862 the glacier theory of the drift was unqualifiedly adopted. 

 Thenceforward the great influence of the Manual of Geology was 

 unquestionably an important factor in the rapid progress of the 

 glacier theory to substantially unanimous acceptance. 



Dana gave much attention to a study of the terraces and other 

 phenomena connected with the melting of the ice sheet, as shown 

 in the vicinity of New Haven and in the Connecticut valley. The 

 results of these studies were given in a number of papers published 

 in the years from 1870 to 1883. While these papers show much of 

 conscientious observation, their conclusions must be considerably 

 modified in the light of more recent studies of the Glacial period. 



The results of another study of Dana's own locality are given 

 in an elegant little volume entitled The Four Rocks of the New 

 Haven Region, published in 1891. In the careful study of East 

 Rock, West Rock, Pine Rock, and Mill Rock, he showed unmis- 

 takably that the trap-rock of these picturesque hills formed intru- 

 sions in the Triassic sandstones. He was, however, in error in 

 extending the same conclusion to the long series of ranges of trap 

 hills from Saltonstall Ridge to Mount Holyoke. Though these 

 hills are topographically similar to the New Haven " Rocks," and 

 consist of similar material, it has been conclusively shown by 

 Davis, Emerson, and others that the trap in them has the relation 

 not of intrusions but of lava sheets outpoured upon the surface. 



With Professor Dana's profound faith in Christianity, he could 

 not be indifferent to the relations of science and religion. Believ- 

 ing that the opening chapters of Genesis contain the record of a 

 divine revelation of the fact of creation, and, in some degree, of 

 the order and method of creation, he could not be satisfied without 



