210 Transactions of the Academy of Science of St. Louis 
The drift may be traced in a broad arc, convex to the north- 
east, to a point about half way between Bethalto and East Alton, 
both in Madison County, Illinois. From here a slightly irregular 
line can be drawn to the conspicuous drift on Otter Creek, 
Jersey County, Illinois. The drift along this line is largely cov- 
ered by loess, but may be traced by a succession of low, broad, 
inconspicuous mounds and by exposures of drift in some cuts. 
Southward from Edwardsville, the drift may be seen not 
far from the Mississippi, bluffs to Caseyville, St. Clair County, 
Illinois. From here southward the boundary of the drift has 
not been re-examined. Leverett’s work indicates that the ice 
front stood approximately parallel to the present bluffs of the 
Mississippi River, but some distance east of them as far south 
as Murphysboro, Jackson County, Illinois, were it turned east- 
- ward beyond the limits of the Middle Mississippi River Region. 
On the flood plain of the Mississippi River, west of Casey- 
ville, there is a group of low, conical hills, most of them 
scarcely reaching a height of 40 feet above the flood plain. 
The highest one, known as Cahokia Mound or Monks Mound, 
reaches an elevation approximately 100 feet above the flood 
plain. These mounds are commonly called Indian Mounds. It 
has been been supposed that they were constructed by human 
agency. It is certain that some, but apparently not all, of the 
mounds were used by some early pre-white inhabitants as burial 
sites. Probably all would agree that the upper portion of 
Cahokia Mound is of artificial construction. Worthen" held that 
the base of this mound, was made of drift clay and was natural. 
Others have disagreed with him. The writer has no additional 
comment save this, if they are of drift clay and natural, their 
location is most significant, being directly in line with the drift 
at Caseyville and at O’Fallon Park, St. Louis. 
THE ILLINOIAN DRIFT IN ST. LOUIS AND 
ST, LOUIS COUNTY 
A thin strip of ice-laid drift may be traced, with some inter- 
ruptions, for a distance of about eight miles along the bluffs 
