508 MORRIS M. LEIGHTON 
in the calcareous zone, representing a concentration of part of the 
lime formerly in the upper portion, are somewhat extreme for 
drift of Illinoian age, underlying calcareous loess. The signifi- 
cance of these evidences seems even greater when one takes note 
of the pebble band at the top and the rounded summit which 
indicate the removal of an unknown amount of the leached drift. 
That this erosion was considerable and took place before the 
deposition of the loess is further suggested by the patchy distri- 
bution of the drift. 
The evidences of great age stimulate a search for the nearest 
known Kansan drift. Drushell describes several exposures of 
much weathered drift, believed to be Kansan, in St. Louis.*7 And 
Fenneman states that the vicinity of St. Louis ‘apparently con- 
tains the thin edge of the Kansan drift sheet,” as well as that of 
the Illinoian drift.2 The Kansan drift of northern Missouri being 
in the Keewatin field, the question arises as to whether the rem- 
nants of drift at Alton may not record the movement of the Kansan 
ice across the site of the present Mississippi Valley. An examina- 
tion of the petrology of the Alton deposits, made with the capable 
help of Dr. T. T. Quirke, supports an affirmative answer. None 
of the pebbles, so far as known, is distinctively from ledges in the 
Labrador field, whereas, all of them may well have come from 
formations in the Keewatin field, a few strongly suggesting native 
ledges at the west end of Lake Superior. 
Some negative evidence, however, is to be considered. Leverett 
has observed two occurrences of glacial striae on bedrock at Alton, 
whose trend is S. 30°-40° W.3 Although referred to the Illinoian 
ice, they were probably made by whatever glacier deposited the 
overlying till. If the drift is Kansan and of Keewatin relationship, 
the ice lobe in northern Missouri must have radiated until the 
eastern peripheral part moved in a northeasterly direction (E. 50° 
60° N.)—a seemingly extreme departure from the main movement 
* Jour. Geol., Vol. XVI (1908), pp. 493-98. 
2‘Geology and Mineral Resources cf the St. Louis Ouadners 2? US) Geol 
Survey, Bulletin 438, p. 31. 
3 Frank Leverett, ‘“‘The Illinois Glacial Lobe,” U.S. Geol. Survey, Monograph 
XXXVIII (1899), pp. 86-87. 
