21 '2 The Aiiirriran (irolor/tKf. N..v.-iiii)or, isoi 
i)t" tlu'sf the facts are essentially the same; the wash was vigorous 
near the iee-edjre and liecame less strong soutliward. 
'riie slojje of the glacial flood plain has been dctcrinincd aj)- 
proxiniately in the most of these instances, and it is found that 
the descent was consi(U'ralily more rajjid than that of the present 
streams near the edge of tlu- ice. hul Ix-yond that the descent was 
only slightly greater than that of the present streams. 
For instance, the terraces which icpi-csenl the glacial flood plain 
on the ui)per Mississipi)i stand, at the mouth of Chippewa river. 
al>out Hid feet al)ov(' the present sti'cain. At the latitude 
of the southern line of Wisconsin. 1 .")(! miles south, the 
terrace is scarcely .")(! t\>et high, indicating a slope of four inches 
to the mile more than the present. IJetween St. liouis and the 
southern extremity of Illinois thi' discrimination of the glacial 
rtoo<l plain from that of the present sti'cam rc(piires attention. 
as it only I'ist's aliout 2.") feet higher and is scarcely ahove the 
extreme reach of modern floods. lielow the mouth of the Ohio 
it is not certain whether the glacial flood [jroducts under con- 
sideration ha VI' Iteen successfully distinguished from deposits 
formed liy the modern ri\-er. lU'clines of a similar nature are 
found on the ^Visconsin. the Kock. the Illinois, tlu' Wahash. tiie 
tributaries of the Allegheny and the .\lleghenv itself. On the 
iiittle and (Jreat .Miamis Mr. Lcvcrctt has found that the glacial 
floiul plains desci'ud less rapiilly than the present streams. 
But before conclusions respecting the slope of the general sur- 
face are drawn, it is to be noted that all these glacial streams 
were di juisitlini and not eroding, and that their currents were not 
suttlcient to enable them to carry away the l)Uiilcn of material 
furnished to them, so that they l)uilt up their liottoins until 
suttlcient slope was gained. The de[)osits of gravel on tlu-se 
streams near tlu- ice-margin, reach in several instances. Iteyond 
10(1 feet in depth. The increased slope of the flood plain near 
iIh' moraine is ol)viously due to the greater load of material and 
not to any upward curvatuic of the general surface. 
These being the essential facts, judgment will perhaps differ 
as to the precise amount of slope which the genei'al surface pri'- 
sentecl at the glacial stage in <iuestioii. but 1 think no one. who 
duly considers the phenomena, will maintain that the slope was 
very much greater than the present. The existing streams aie 
erodinu' their bottoms, even with theii' lower uradient. and llie 
