318 POPULAR SCIENCE MONTHLY 



review of his opinions may be given in some detail. Beginning with 

 the later Tertiary times, he believed the following sequence of events 

 to have been established. 



(a) During Miocene and Pliocene epochs a continent several hun- 

 dred feet lower than now, the ocean reaching to Louisville and Iowa, 

 with a subtropical climate prevailing over the lake region, the climate 

 of Greenland and Alaska being as mild as that of southern Ohio at 

 present. 



(&) A preglacial epoch of gradual continental elevation, which 

 culminated in the glacial epoch, when the climate of Ohio was similar 

 to that of Greenland at present, and glaciers covered a large part of 

 the surface down to the parallel of forty degrees. 



(c) This period followed by another interval of continental sub- 

 sidence characterized by a warmer climate and melting glaciers and 

 by inland fresh-water seas filling the lake basins, in which were de- 

 posited the Erie and Champlain clays, sands and boulders. 



(d) Another epoch of elevation which is still in progress. 



The sheet of clay and boulders which was found directly overlying 

 the polished surface of the rocks over so large a part of the state, now 

 known under the name of till and boulder clay, he described under the 

 general name of glacial drift, while the loose boulders which he found 

 scattered indiscriminately over the surface, frequently resting on the 

 fine stratified clays, were known under the name of iceberg drift. 



If, he wrote, we restore in imagination this inland sea, which we 

 have proved once filled the basin of the lakes, gradually displacing the 

 retreating glaciers, we are inevitably led to a time in the history of 

 this region when the southern shore of this sea was formed by the 

 highlands of Ohio, etc., the northern shore a wall of ice resting on the 

 hills of crystalline and trappean rocks about Lake Superior and Lake 

 Huron. 



From this ice wall masses must from time to time have been detached, 

 just as they are now detached from the Humboldt glacier, and floated off south- 

 ward with the current, bearing in their grasp sand, gravel and boulders — 

 whatever composed the beach from which they sailed. Five hundred miles 

 south they grounded upon the southern shore — the highlands of now western 

 New York, Pennsylvania and Ohio, or the shallows of the prairie region of 

 Indiana, Illinois and Iowa. There melting away and depositing their entire 

 loads. 



The loess, as one would naturally expect from the foregoing, was 

 looked upon as the finer sediment deposited in the quiet waters of one 

 of these inland seas, to which the icebergs had no access. The lake 

 basins, with the exception of that of Lake Superior, were regarded as 

 excavated by glacial action — thus agreeing with Logan. 



The views of Orton, who succeeded Newberry as state geologist, 

 were not widely different, and, briefly expressed, were as follows : 



Threefold divisions of glacial time may be considered as demon- 



