JAMES DWIGHT DANA. 617 
cialists of different opinions in America, and he took the greatest 
pains to get from original sources the evidence on both sides. 
He opened the pages of the Journal of Science to discussion of both 
views. His correspondence was widely extended, and with, I 
presume, every one of those who had taken a prominent part in 
the discussions of the past few years. In a conversation with 
the writer on one of those days, he remarked that one of the 
chief causes of contrary opinions regarding the division of the 
glacial period in America was, he believed, due to local coloring 
resulting from taking either the phenomena of New England and 
the eastern edge of the glacier, or else those of the western- 
central region, as the standards of judgment by the two sides in 
the discussions. 
When he had finished the pages on the quaternary for the 
printers, he remarked that he had reached an explanation of the 
events which he thought would harmonize the divergent views, 
and he expressed more than ordinary enthusiasm, and spoke as 
if, having exhaustively compared all the facts that had been 
brought forward, he had reached what he believed to be the true 
solution of the vexing problem. 
His explanation of the case, viz.,an epoch of extreme advance, 
which was of great length, with, following, an epoch of first 
retreat, then halt, in which the deposits of the Lafayette forma- 
tions were being made on the gulf and eastern borders, and with, 
third, the epoch of final retreat of the ice from the northeastern 
plateau, is certainly a comprehensive interpretation of the series of 
phenomena as a whole, however it may be modified by increasing 
knowledge. (See Manual of Geology, 4th ed., pp. 943-80.) 
The clearing up of the confusion involved in Emmons’ 
“Taconic System,” was another task to which Professor Dana 
gave enthusiastic attention. After some thirty years of defense 
of the system by its friends, against the ineffective attacks of 
those who were unable to bring convincing proof of its fallacies, 
Professor Dana entered the field in 1871. The main trouble was 
that Emmons’ interpretation was based upon several false tenets 
which were then maintained by the best of geologists ; and it was 
