76 PROCEEDINGS OF THE PHILADELPHIA MEETING 



PHYSIOGRAPHIC STUDIES IN THE DRIFTLESS AREA 

 BY ARTHUB C. TROWBRIDGE 



(Abstract) 



Physiographic work done aud iu progress in northwestern Illinois, north- 

 eastern Iowa, southeastern Minnesota, and portions of Wisconsin, under the 

 auspices of the University of Iowa, the University of Chicago, aud the Geolog- 

 ical Surveys of Iowa and Illinois, is yielding new data on the history of the 

 driftless area. 



The data so far gathered belong under three heads: (1) The Upland Plains, 

 (2) The Glacial Drifts, and (3) The History of Drainage. 



There are two upland plains, both of which are old peneplains. The highest 

 and oldest one slopes from 1,500 feet above tide at Baraboo, Wisconsin, to 

 1,200 feet at Dubuque, Iowa, and cuts across from Huronian quartzite at 

 Baraboo to Niagarau dolomite at Dubuque. Evidence points to the late Ter- 

 tiary age of this plain. The younger peneplain has been traced from Jo Daviess 

 County, Illinois, where it lies on Maquoketa shale and Galena dolomite at an 

 altitude of 900 feet, to New Albin, Iowa, at which poiut it has an altitude of 

 1,100 feet and lies on the Prairie du Chien formation. Pre-Kansau glacial 

 drift found on this plain iu Iowa places its age as early Pleistocene. 



The glacial drifts of the region include (1) pre-Kansan drift on the Pleisto- 

 cene peneplain in Iowa, (2) Kansau Valley trains in tributaries to the Mis- 

 sissippi from the west, (3) Illinoisan drift on the east border of the driftless 

 area in Illinois, (4) Wisconsin till in Wisconsin and fluvo-glacial material of 

 the same age in the main valleys throughout the area, and (5) weathered till 

 aud fluvio-glacial material of unknown age and derivation at Bridgeport, Wis- 

 consin. 



A study of drainage lines has led to the discovery of new data on the 

 Pleistocene history of the area. For instance, the Upper Iowa River iu Iowa 

 cut a valley 600 feet deep during the Aftonian interglacial epoch. Couler 

 Valley, at Dubuque, has ahso an interesting history, which throws light on the 

 duration of interglacial epochs. There is no evidence of a pre-Pleistocene Mis- 

 sissippi River. The Mississippi gorge was cut from a level of 900 feet at 

 Dubuque to 276 feet at the same place, between Jerseyau aud Wisconsin times, 

 and the stream is now at grade ou Wisconsin material 324 feet above its pre- 

 Wisconsin level. 



This work will be carried further during the coming and following years. 



Presented by title in the absence of the author. 



HEMWONES AT THE MOUTHS OF HANOINO VALLEYS 

 BY CHARLES E. DECKER * 



(Ahstract) 



On the south side of Lake Erie numerous small streams tributary to the 

 larger creeks enter the main valleys through hanging valleys. Similarly, some 

 of the small streams east of Erie, Pennsylvania, enter the lake through hang- 



