666 THE ICE AGE LY NORTH AMERICA, 



to occupy this locality, so soon after it was uncovered from the 

 ice, was their discovery of the quartz-veins in the slate there 

 and on the Little Elk Kiver, affording suitable material for 

 making sharp-edged stone implements of the best quality. 

 Quartz-veins are absent or very rare and unsuited for this use 

 in all the rock-outcrops of the south half of Minnesota that 

 had become uncovered from the ice, as well as of the whole 

 Mississippi basin southward, and this was the first spot acces- 

 sible whence quartz for implement-making could be obtained. 

 While the deposition of the valley-drift at Little Falls was still 

 going forward, men resorted there, and left, as the remnants 

 of their manufacture of stone implements, multitudes of quartz 

 fragments. By the continued deposition of the modified drift, 

 lifting the river upon the surface of its glacial flood-plain, 

 these quartz-chips were deeply buried in that formation. The 

 date of this valley-drift must be that of the retreat of the ice 

 of the last Glacial epoch, from whose melting were supplied 

 both this sediment and the floods by which it was brought. 

 The glacial flood-plain, beneath whose surface the quartz frag- 

 ments occur, was deposited in the same manner as additions 

 are now made to the surface of the bottom-land ; and the 

 flooded condition of the river, by which this was done, was 

 doubtless maintained through all the warm portion of the year, 

 while the ice-sheet was being melted away upon the region of 

 its head- waters. But in spring, autumn, and winter, or, in 

 exceptional years, through much of the summer, it seems prob- 

 able that the river was confined to a channel, being of insuffi- 

 cient volume to cover its flood-plain. At such time this plain 

 was the site of human habitations and industry. After the 

 complete disappearance of the ice from the basin of the upper 

 Mississippi, the supply of both water and sediment was so 

 diminished that the river, from that time till now, has been 

 occupied more in erosion than in deposition, and has cut its 

 channel far below the level at which it then flowed, excavating 

 and carrying to the Gulf of Mexico a great part of its glacial 

 flood-plain, the remnants of which are seen as high terraces or 

 plains upon each side of the river. 



The question concerning the manner in which human 

 remains have become incorporated in the glacial gravels is 





