3 i8 THE POPULAR SCIENCE MONTHLY. 



tion, and especially the history of the entire Glacial epoch. The 

 members of the Geological Survey engaged upon the general work 

 were only to a limited extent occupied with this problem. In the 

 special fields where they were engaged in studying the primeval 

 foundation rocks they also studied the glacial formations and the 

 modern overplacements. But the field was very large, and many 

 geologists in the country had already made observations and en- 

 gaged in researches of this character. Most of these geologists 

 were professors in the various colleges of the country, and it was 

 decided by the director to enlist these professorial geologists as 

 far as possible to continue the work and solve these problems for 

 the general survey of the United States upon the foundation of 

 observation already begun by them. For this purpose Prof. 

 Chamberlin, then of Beloit College, with Prof. Salisbury, his asso- 

 ciate, and many other professorial assistants, were engaged upon 

 the work. Prof. Shaler, of Harvard University, was also enlisted, 

 with a large corps of assistants. Prof. Emerson, of Amherst Col- 

 lege, was likewise enlisted, with his assistants ; and Prof. Davis, 

 of Harvard University, with his assistants, also took a part. Mr. 

 Gilbert, of the Geological Survey, with his assistants, was study- 

 ing the lake basins of the far West, but, as their history was in- 

 volved in the history of the glacial formations, he incidentally 

 took part in this work. Mr. McGee, permanently employed upon 

 the survey, with his assistants, was engaged in studying the 

 estuarine and coastal-plain formations of the Atlantic slope, and 

 he soon discovered that they were involved with the glacial de- 

 posits that had come down from the Appalachian Mountains. 

 Besides the men thus occupied, many other volunteers, as pro- 

 fessors and students, took part in the work, now here, now there ; 

 so that altogether more than fifty different men engaged in the 

 solving of these great problems. Nearly all the men who engaged 

 in this work soon discovered that the preliminary problem was to 

 formulate the criteria by which modern overplacement is to be 

 distinguished from original glacial formation. As this proceeded 

 it was further discovered that much of the confusion in the study 

 of the glacial rocks themselves was cleared away, and that it was 

 possible to read the record of the old Glacial epoch in such a 

 manner as to discover its history. 



So the work went on year after year, in small part by the regu- 

 lar employees of the survey, in chief part by a professorial corps, 

 aided by many volunteers, often university students. Then many 

 of the State geologists were enlisted, and the work proceeded, 

 until at last a vast body of facts has been collected. The men 

 often conferred with one another and visited doubtful points to- 

 gether. The officers of the Geological Survey, the professorial 

 geologists, and the State geologists thus associated themselves 



