254 MAN ANB THE GLACIAL PERIOD. 



Upham lias pretty clearly shown that the gravel of the 

 terrace overlying them was mostly deposited while the ice- 



^feifw?^ Terrace of JiC^ficd Drift, I 





Fig. 73.— Section across the Mississippi Valley at Little Falls, Minnesota, show- 

 ing the stratum in which chipped quartz fragments were found by Miss F. E. 

 Babbitt, as described in the text (Upham). 



front was still lingering about sixty miles farther north, 

 in the vicinity of Itasca Lake.* 



Up to this time the above are all the instances in which 

 the relics of man are directly and indubitably connected 

 with deposits of this particular period east of the Eocky 

 Mountains. Probably it is incorrect to speak of these as 

 preglacial, for the portion of the period at which the de- 

 posits incorporating human relics were made is well on 

 towards the close of the great Ice age, since these terraces 

 were, in some cases, and may have been in all cases, depos- 

 ited after the ice-front had withdrawn nearly, if not quite, 

 to the water-shed of the St Lawrence basin. It may be 

 difficult to demonstrate this with reference to the gravel 

 deposits at Trenton, Madisonville, and Medora, but it is 

 evident at a glance in the case of Xewcomerstown and 

 Little Falls. 



That the implement-bearing gravel of Trenton, N. J., 

 belongs to the later stages of the Glacial period is evident 

 from its relation to what Professor H. Oarvill Lewis called 

 " the Philadelphia red gravel and brick-clay," but which, 

 from its large development in the District of Columbia at 

 Washington, is called by Mr. McG-ee the " Columbia de- 

 posit." The city of Philadelphia is built upon this forma- 

 tion in the Delaware Valley, and the brick for its houses 

 is obtained from it ; the cellar of each house ordinarily 

 furnishing clay enough for its brick walls. This clay is 



* For a general map, see p. 66 ; also p. 225. 



