232 Transactions of the Academy of Science of St. Louis 
thickness of fine glacial flour was deposited as a blue clay. In 
at least one spot near Elm Point a mastodon was mired in the 
blue clay. 
The Missouri River, being dammed and still receiving large 
quantities of sediment from its headwaters, rapidly accumulated 
sediment in thick layers. Thus was produced the Boeuf Terrace. 
This accumulation may very probably have occurred rapidly and 
it is not necessary to believe that the river was blockaded for 
any great length of time. As these sediments were being ac- 
cumulated, the ice front probably formed at least part of the 
northern, as well as the northeastern, shore of the lake. From 
this ice front icebergs escaped, and floating over the surface 
of the lake and melting, deposited whatever cobbles, boulders, 
and other detritus they contained, in the midst of the accumu- 
lating silt in the bottom of the lake. 
It seems probable, but not certain, that the pre-Illinoian 
drift in St. Louis is of Kansan age. The drift is probably from 
the Kewatin center. If this is true, it would seem probable that 
some of the ice from Lincoln County which crossed the Missouri 
River continued southeastward, depositing the drift now found 
in the City of St. Louis. 
Leighton3? has suspected that the drift at Alton was of Kan- 
san age and that it came from the southwest, that in some way 
an extension of the Lincoln County ice sheet swung in this direc- 
tion. He thought that this would account for cerain striations 
of the limestone at Alton, recorded by Leverett.33 If Leighton 
is correct, then it would seem that the Mississippi River, at that 
time occupying the present course of the Illinois River, must 
have been dammed above Alton, and that a terrace correspond- 
ing in some respects to the Boeuf Terrace should be traceable 
in the Illinois River as it is in the Missouri River. The investiga- 
tion has not yet been carried far enough to check this point. 
With the retreat of the Kansan ice in Yarmouth time, the 
Missouri River started eroding the Boeuf Terrace, and now 
