Drushel — Glacial Geology in St. Louis and Vicinity. 35 



on the contact, will cover typical material of the two 

 formations. These contacts are equally sharp in a sec- 

 tion twenty rods or more np the main stream. 



The stratified clay in this section argues the presence 

 of two drift sheets. The material in both these sheets 

 differs from the Chain of Rocks material in that the lat- 

 ter has fluvio-glacial characteristics. The bowlders of 

 the latter are chiefly granite, relatively few of which 

 are thoroughly weathered. In the former the erratics 

 are chiefly Sioux quartzite, the granites always being 

 much weathered. It is probable that the drift below the 

 clay is pre-Kansan, and that above the clay is Kansan, 

 the Illinoian being represented by the outwash in the 

 Chain of Rocks bluffs. 



SUMMARY. 



1. A thin mantle of Kansan and possibly pre-Kansan 

 drift, at one time covered the St. Louis region. 



2. The present patches are to be accounted for on the 

 basis of erosion previous to loess deposition. 



3. Drift of considerable thickness reached latitude 

 38° 34'. 



4. The drift two miles north of the Chain of Rocks rep- 

 resents remnants of the Kansan and possibly the pre- 

 Kansan. 



5. The Illinoian lobe occupied the Mississippi flood- 

 plain to a great depth near the Chain of Rocks, and 

 probably pushed into St. Louis County. 



6. That portion of the Chain of Rocks bluffs which is 

 drift should be regarded as outwash from the Illinoian 

 lobe. 



7. Careful search may reveal Kansan drift elsewhere 

 in Missouri south of the Missouri River. 



