648 UEPORT— 1891. 



Claymont, Delaware, by Dr. II. T. Cresson ; at Newcomerstown, Ohio, by Mr. 

 W. C. Mills ; at Loveland and Madisonville, Ohio, by Dr. M. C. Metz ; at Medora, 

 Indiana, by Dr. Cresson ; and at Little Falls, Minnesota, by Miss Babbitt. The 

 determination of the age of these implements requires a general study of the Glacial 

 phenomena of the continent. 



Through the combined labours of many observers, the southern boundary of 

 the glaciated region has been carefully traced across the continent, and found to 

 run in an irregular course from the vicinity of New York City, south-westward 

 through Cincinnati in Ohio, to Carbondale, about latitude 38°, in southern Illinois, 

 Thence it bears north-westward, following approximately the course of the Mis- 

 souri River, and entering Canada a hundred miles or mora east of the Rocky 

 Mountains. The centre of radiation for this portion of the ice-lield was in the 

 vicinity of the south-east of Hudson Bay, and this portion has been named the 

 Laurentide glacier. From that centre the ice movement was west and north, as 

 well as east and south. 



Whether the Laurentide glacier became confluent on the west with the 

 Cordilleran glacier, which occupied the vast region in British Columbia west of 

 the Rocky Mountains, is still in dispute. But it is certain that the ice from that 

 centre, as well as in the mountains of southern Alaska, moved outward in all 

 directions. The glaciation of the Rocky Mountains, and of the Cascade Range 

 south of the Canadian boundary, was comparatively slight. 



The distribution of ice during the Glacial period in Xorth America bears 

 strongly against all theories which attribute the phenomena to cosmical causes. 

 There was not a Polar ice-cap, but an accumulation about centres mainly south of 

 the Arctic Circle. While there is accumulating evidence pointing to an extensive 

 elevation of the glaciated areas during the latter part of the Tertiary period, and 

 of a subsidence at the same time of the Isthmus of Panama. The valleys occupied 

 by the great lakes were probably mainly formed by erosion during that period 

 of elevation, the old lines of drainage having been closed up by the debris of the 

 Glacial period. This is clearly the case with Lake Erie, and, to a large extent, 

 may be the case with the other lakes. There are positive signs of such old 

 channels, now buried, leading to the Mississippi from Lake 3Iichigan, and to the 

 Hudson from Lake Ontario. 



The Palicolithic implements discovered in North America are from the terraces 

 of streams flowing outward from the glaciated region — namely, the Delaware, ou 

 the Atlantic coast, the Tuscarawas, the Little Miami, and the "White, in the 

 Valley of the Ohio, and the Upper Mississippi. Similar terraces are universal 

 along the streams flowing out of the glaciated region, and are composed mainly of 

 material which was first transported from the distant north by Glacial ice. They 

 are doubtless the deposits occurring during the floods which characterised the 

 closing portion of the Glacial period. Associated with these implements are the 

 bones of the mammoth and some other animals, now either wholly extinct, or 

 extinct in that region. In New Jersey the bones of several Arctic species have 

 been found. 



The approximate date of these closing scenes of the Glacial period seems pretty 

 clearly to be indicated by the recession of the Falls of Niagara and of St. Anthonj', 

 where the conditions are uniform, and the length of the gorges, as well as the rate 

 of recession, known. In both cases the length is a little over seven miles, and the 

 rate has been ascertaired to be between 3 feet and 5 feet per year. The streams 

 cannot have been at their work of erosion in those channels much more than 

 10,000 years. A similar result is obtained independently from calculations 

 respecting the enlargement of post-Glacial valleys, the erosion of the banks of 

 Lake Michigan, and the post-Glacial silting-up of many small lakes. But how- 

 much earlier than this man's advent on the continent may have occurred it is not 

 so easy to determine. 



The extent of post-Glacial subsidence is much disputed, and has important 

 bearings on the question of the continuity of Glacial man with the races now 

 occupying the continent. The post-Glacial subsidence, of which there seems to be 

 eufficient evidence, amounts only to about 500 feet in the lower axis of the 



