Drushel — Glacial Geology in St. Louis and Vicinity. 31 



total 102. Of this number twenty-one are longer than 

 ten centimeters, and fifty-two are igneous. A granite 

 bowlder weighing ninety-five pounds was obtained from 

 this section. (See Fig. 5.) Igneous bowlders of ten to 

 fifteen pounds in weight, lying near the top of the de- 

 posit are rather common. These bowlders show the char- 

 acteristic glacial planing, polishing, and occasional stri- 

 ation. (See Fig. 4.) Now and then a planed granite 

 bowlder is weathered so much as to enable one to shatter 

 it with a light tap of the hammer. (See Fig. 4.) How- 

 ever, as a rule, the pebbles and bowlders appear quite 

 fresh, as compared with drift elsewhere in St. Louis. 

 (SeeFigs. 3, 4, 5, 8and9.) 



The deposit just described is, as a whole, much less 

 weathered and more sandy than the other St. Louis drift 

 and the drift north of the Chain of Rocks. This long 

 ridge should probably be interpreted as an outwash of 

 the Illinoian lobe when it occupied the Mississippi flood 

 plain in this region. Such an interpretation would ac- 

 count for the general contour, for the slight stratification 

 and for the grading of the material from coarse pebbles 

 to sand with small pebbles in an east to west section of 

 the deposit, as determined by the gullies on both sides 

 of the bluff. 



Leverett,^ not admitting the existence of Illinoian drift 

 in St. Louis County, has suggested the possibility of an 

 encroachment in the vicinity of St. Louis by the Illinoian 

 ice sheet. *' Possibly the Mississippi Valley was en- 

 croached upon for a few miles in the vicinity of St. 

 Louis, Mo. There appears to have been at most only a 

 partial blockade near St. Louis. An examination into the 

 character of the deposits in the Mississippi Valley, be- 

 tween Fort Madison and St. Louis, has brought to light 

 nothing to indicate vigorous drainage at the Illinoian 

 stage of glaciation. Indeed, the valley seems to have be- 



*F. Leverett. U. S. Geol. Surv. Monograph 38:64, 71. 1899. The 

 Illinois Glacial Lobe. 



