SUPERFICIAL DEPOSITS ALONG THE 
MISSISSIPPI 
GERARD FOWKE. 
For the most part geologists, and others, who have studied 
the loess formation in the states bordering on the Missouri and 
Mississippi rivers, concur in attributing the deposit to glacial 
floods which attained their maximum when the ice was melting 
along the front more rapidly than it could advance from the north. 
The material is clay and sand, in varying proportions, modified 
more or less by local detritus. Considering the ease with which 
it is excavated, its power to withstand pressure or erosion is some- 
thing remarkable. This quality is especially noticeable along the 
iit sso ur bluffs; below that river it becomes less resistant. On the 
upper portions of the two great rivers, the loess is heavy, forming 
high bluffs and spreading far inland; southward, it progressively 
diminishes in extent and thickness. This fact, reinforced by 
similar conditions observable along tributary streams, have enabled 
students to determine that coincident with the greatest extension 
of the glacier, and lasting until the present time, there was a 
marked subsidence of land, relative to sea-level, in the Mississippi 
Valley; the subsidence being more pronounced toward the north. 
The current of southward flowing streams was retarded, and the 
sediment-laden waters began to free themselves from. silt, by 
precipitation, almost at once upon their emergence from the ice. 
There was still sufficient movement, however, to carry the finer 
suspended matter until sea-level was reached. 
The limit of the ice-sheet, in southern Illinois, was along the 
hills bordering Big Muddy on the north, almost to the mouth of 
that stream, as it passed into the Mississippi at Grand Tower; 
thence northward, closely following the line of the larger stream, 
nearly to Alton; thence, crossing into Missouri, it skirted the north 
side of the Missouri river nearly to the middle of the state. On 
the bluffs at the mouth of the Missouri, on the south side, is con- 
siderable glacial drift; until very recently it has been uncertain 
whether it marked an extension of the glacier, or whether it is due 
to floating ice. Within the past year, the excessive rainfall has 
enabled two little streams to carry away enough overlying gravel 
to reveal two small areas of typical till; so it is now certain that 
the main body of ice shut off the Missouri and consequently acted 
as a temporary dam. Further, Brodhead records the occurrence 
of gravel, which he supposed to be of glacial origin, on the highest 
point in St. Louis county, about 350 feet above the Mississippi. eG 
seemed possible, from these facts, that the ice had attained sufficient 
height to back the water up the Missouri a long distance and 
