1882 .] 
353 
[Davis. 
it in some way by descent, but the precise relationship is not yet 
made out. 1 
Wisconsin seems to have had a similar glacial lake about Fond 
du Lac 2 ; it is curious to find that its descendant and that of Lake 
Agassiz have the same derivation, physical as well as etymological, 
and the Fox and Rock rivers 3 are related much in the same way 
as the Red and the Minnesota. Northwestern Ohio, and a stretch 
of flat country east and west, received its surface covering of 
stratified clays from a great body of water, dammed on the north 
most probably by the retreating ice, and determined at its high- 
est level by the elevation of certain “ waste weirs” on the south. 4 
The flat prairies south of Lake Michigan are of the same origin. 5 
Further study of this region will give a most interesting chapter in 
our surface geology and physical geography. The absence of 
similar plains in New England must be explained by the fact that 
here the ice-sheet ended on groun 1 sloping to the south, so there 
was no opportunity for a large body of water to collect against it: 
our eastern prairies are under the ocean. We have, however, in 
the snnd-plains that are common in these eastern states, evidence of 
the former existence of small lakes probably of this origin at least 
in part (see C. 4, 13). 6 About the margin of Lake Superior there 
are many sand terraces marking old shores, some of which are 
two or three hundred feet over the present surface, and although 
these have not been traced all around the lake-border, they are 
generally taken as evidence of a former level of the whole lake. 
It seems safer to attribute some of them at least to local bodies 
of water between the lake-shore and the retreating ice : the same 
suggestion may have some application to the other Great Lakes as 
1 G. K. Warren, in U. S. Chief of Engineer’s Report, 1868, 307, shows probable 
former area of lake, suggests glacial barrier and northern depression as its cause, and 
explains large size of the Minnesota valley. An abstract of a later report with maps 
is given in Amer. Journ. Sci., xvi, 1878, 417. N. H. Winchell, Popular Sci. Monthly, 
in, 1873, 295. G. M. Dawson, Geol. and Resources of the 49th Parallel, 1875, 253. W. 
Upham, Geol. Minn. Reports, 1879, 1880, explains and names the lake and gives many 
additional details, with a map of the moraines. 
2 Chamberlain, Geol. Wise, ii, 1877, 137. 
3 E. Andrews, Am. Journ. Sci., xliii, 1869, 172. 
4 Newberry, Geol. Ohio, ir, 29, 51. 
5 Winchell, Pop. Sci. Monthly, in, 1873, 295. 
6 For example, Upham, Geol. New Hampshire, hi, 11, 115, etc., and maps. 
PROCEEDINGS B. S. N. H. VOL. XXI. 23 JUNE, 1882. 
