358 G. F. Wright — Unity of the Glacial Epoch. 



Talley, is now found to be equally characteristic of the region 

 east of the Alleghenies. 



3. The lack of drumlins and other ridged accumulations 

 along the glaciated border need indicate only a small amount 

 of ice movement over the region, or a depressed slack condi- 

 tion of drainage which, as already stated, may be supposed in 

 case of one glacial period as well as of two. 



4. The feebleness of glacial erosion over the fringe follows 

 from the reasons already stated. Of course there was less 

 movement over the fringe than farther back. Still that there 

 was some vigorous movement close to the very margin is 

 shown by the glacial strise which I have reported from Car- 

 bondale, 111. and from St. Louis, Mo. (See Bull. Geo! Surv., No. 

 58, pp. 71-73). Dr. Max Foshay has also discovered very pro- 

 nounced groovings in Western Pennsylvania in the area cov- 

 ered by the fringe several miles south of the moraine as there 

 laid down by Professor Lewis and myself. 



5. The fifth point is in part a mere repetition of the first, 

 and to some extent the reply will be the same. The slack 

 drainage indicated in the deposits near the border was caused 

 probably by the changes of level which have been connected 

 with the Champlain epoch. A part of this evidence of slack 

 drainage is found along the Susquehanna and Delaware Val- 

 leys, in the Columbia deposits of Mr. McGee. A natural sup- 

 position is that the climax of the period was characterized by 

 a depression of land considerably greater than is indicated by 

 the level of the deposits in the Champlain Yalley at the time 

 of the disappearance of the ice. But as this point involves a 

 theory concerning the cause of the period and of the changes 

 of level attending it, a few paragraphs may well be devoted 

 to a fuller statement of the reasons for believing that a sub- 

 sidence may naturally be supposed to have attended the climax 

 of the epoch on the supposition that it was single. 



Whatever subsidiary aid the eccentricity of the earth's orbit 

 may provide for the production of glacial conditions, there is 

 now little doubt that the ice age was introduced and closed 

 by marked changes of level, both in North America and in 

 Northern Europe. The fiords which characterize the coast of 

 Norway, and which are brought to light by the sounding line 

 along both the Atlantic and the Pacific coast of North 

 America bear striking witness to the extent of this elevation 

 during the period just preceding the glacial epoch. (See 

 Appendix to The Ice Age in N. A by Warren Upham.) So 

 great was this late Pliocene elevation that it seems to many 

 that it might have been sufficient to have produced the glacial 

 conditions of the succeeding age even without the aid of astro- 

 nomical changes. An elevation of 3,000 feet would probably 



