350 OHIO STATE ACADEMY OF SCIENCE 
form a temporary lake. But Brodhead’s gravel beds prove to be 
of local origin, while the first-mentioned drift reaches but little, if 
any, more than 100 feet above the stream, and the ice-dam did not 
hold for a period that allowed any channel tobe made to the south 
of it: so another cause must be sought for the loess deposits in the 
vicinity. 
In and around St. Louis the loess forms a cap, covering nearly 
all the early formations. While it is thin on hilltops and thicker 
in valleys by reason of erosion and re-deposition on uneven ground, 
yet it is singularly regular over many square miles. Reports of 
railway cuttings, wells, and other excav ations, contain numerous 
references to “loess 12 or 14 feet thick.” It is from 6 to 8 feet 
thick on a plateau nearly 350 feet high; and is not more than 20 
feet. in most of the county unless near the foot of a slope. This 
means a depth of water that would submerge hills at the level 
indicated, and lowering so rapidly in the end as to uncover all the 
territory within a comparatively short time. 
Worthen says that in Jackson county (Illinois), the loess 
occupies only a narrow belt on the top of the river bluffs; and in 
Union county, next south of Jackson it was found at only one 
point and that below the top of the bluff. 
Shumard notes the presence at Wittenberg, Missouri, of a 
mass of granite weighing several tons; and thinks this is evidence 
of a ledge of eruptive rock in the neighborhood. 
It should be stated that Big Muddy separates Jackson from 
Union county, and that W ittenberg lies opposite to the old mouth; 
being about eighty miles south of St. Louis. Between these two 
points are Rock Creek, twenty miles south of the city, in whose 
valley the loess (modified by local drift) is one hundred feet high ; 
and Plattin creek, forty miles south, where it covers a slope at. an 
elevation of eighty feet. 
It seemed plausible to suppose that a prolongation or spur of 
the glacier might have reached from the Big Muddy to the Mis- 
souri side, thus choking the Mississippi and allowing the water 
to stand at a level sufficient to drown most of the country above. 
Additional color was given to this supposition by the gorge at 
Grand Tower, just below Wittenberg. Here, the river flows in a 
narraw, rock-bound channel, over a solid rock bottom, while on the 
Illinois side is a valley fully three miles wide, of alluvial silt 
subject to overflow in great freshets. But the granite proves to be 
only a boulder, lying in a small ravine a few feet above the river’s 
ordinary level, and it may have come in with an ice floe at any 
time. And there is not a trace of evidence on either side of the 
river, that the glacier had even reached the lowland. This was 
an additional problem, instead of an explanation; for there was 
St. Louis and Cairo only sand and silt are found along the valley, 
a feature that apparently indicates a drainage no more vigorous 
