230 The American Naturalist. [March, 
south toward its former limits. This part of the Ice age is well 
denominated, from its envelopment of the land by ice-sheets, 
the Glacial epoch. Its chief cause I think to have been uplifts 
of the glaciated regions thousands of feet above their present 
height. 
Forest beds and other fossiliferous deposits of the interglacial 
stage in this epoch are found frequently, and on some large 
tracts almost continuously, occurring between deposits of the 
till or glacial drift penetrated by wells, from southeastern 
Ohio, through Indiana and Illinois, to northeastern Iowa and 
to Mower county in southern Minnesota.” Less frequent, but 
still sometimes occupying considerable tracts as shown by 
several wells near together, these interglacial beds are recorded 
by my notes of wells in Lyon, Renville, and McLeod counties, 
Minn., 60 to 90 miles north from the south line of this state. 
More rare instances of their observation are noted as far north 
as in Mitchell township, Wilkin county, and Barnesville in 
the south edge of Clay county, Minn.; and these most north- 
ern localities are situated within the area of the glacial lake 
Agassiz, respectively about 100 feet and 75 feet below its high- 
est and earliest or Herman beach. If the altitude and slopes 
of the land had been then the same as now, an interglacial 
lake, held by the barrier of the receding ice-sheet, must have 
forbidden the growth of forests or formation of swamp deposits 
there, until the outlet was deeply eroded or much farther 
glacial recession permitted that lake to be drained away north- 
ward. Under those conditions an interglacial forest at Barnes- 
ville would imply probably three to six times more glacial 
melting and recession than otherwise would suffice to account 
* Charles Whittlesey, Smithsonian Contributions, No. 197,in vol. xv, 1864, pp- 
13-15. 
J. S. Newberry, Geology of Ohio, vol. ii, 1874, pp. 30-33. 
G. F. Wright, The Ice Age in North America, 1889, pp. 475-496. 
Frank Leverett, Proc. Boston Soc. Nat. Hist., vol. xxiv, pp. 455-459, Jan. 1, 
1890; Journal of Geology, vol. i, pp. 129-146, with map, Feb.—March, 1893. 
W J McGee, Eleventh An. Rep., U. S. Geol. Survey, for 1889-’90, Part I, pp- 
486-496. 
N. H. Winchell, Proc. A. A. A. S., vol. xxiv, for 1875, Part II, pp. 43-56; 
Geology of Minnesota, Final Report, vol. i, 1884, pp. 313, 363, 390. 
