THE 
AMERICAN GEOLOGIST 
Vol. VIII. NOVEMBEE, 1891. No. 5. 
THE ATTITUDE OF THE EASTERN AND CENTRAL 
PORTIONS OF THE UNITED STATES DURING 
THE GLACIAL PERIOD.* 
By T. C. Chambeklin, Mtidisoii, Wis. 
Aside from the inherent interest which lies in the determination 
of any general fact in geology, a special interest attaches to the 
determination of the attitnde of the glaciated area during the ice 
invasions because of its hearing upon their explanation. I pro- 
pose to discuss hypotheses of the cause of the glacial period in a 
separate paper; my present effort will he merely to set foi'th, 
somewhat synoptically, the leading phenomena, and the conclus- 
ions I draw, relative to the attitude of the eastern and central 
portions of the United States during that period. The sjjecial 
data appealed to have l)een gathered chiefly by the members of 
the glacial division of the United States Geological Survey, largely 
by Messrs. Salisl>ur3', J^everett and myself. 
/. Ghi(i()-t^)iiial deposits of tJic lowcf Mississi/ij)i nilh i/. The 
material of the lower Mississippi valley derived from glacial 
waters is divided into two sharply distinct classes; tirst and old- 
est, that which caps the Itlutfs of the Mississippi and mantles all 
the upland for 5(1 miles or more l>ack on the east and which 
occupies the summit of Crowley s ridge that rises from the midst 
of the Mississippi bottoms in Arkansas. The second division 
occupies the trench in which the presiMil liottoms lie and rises but 
♦Read before Section E, Am. Association for the Advancement of 
Science at the Washington meeting, August, 1891. 
