90 PROCEEDINGS OF THE A XX ARBOR MEETIXG 



bearing lead and zinc sulphides were introduced along the early normal faults, 

 and spread out in the Mississippian and lower Pennsylvanian limestones. 

 When they were introduced the nearby limestones were extensively altered 

 to dolomite. Later (middle Tertiary?) a second system of normal faults of 

 northwest trend and northeast dip broke the early faults and ore bodies. 

 Finally, in late Tertiary time, there were sporadic normal faults of small dis- 

 placement. 



The present range is not limited by normal faults and it is therefore not a 

 fault-block range. The poorly defined scarp that forms the eastern front is 

 due to erosion acting on the relatively soft Jurassic sandstone which underlies 

 the Cambrian dolomite thrust upon it. Potosi Peak (8.504 feet), the highest 

 peak in the southern part of the range, coincides with a large thrust block 

 and is limited northeastward by a late normal fault. 



Presented in fnll extemporaneously. 



Brief remarks were made by Messrs. Hill and Lawson, with reply by 

 the author. 



PLEISTOCEXE OF XORTHWESTERX ILLIXOIS: A GRAPHIC PRESEXTATIOX OF 

 SOME OF THE CHIEF LIXES OF EVIDEXCE 



BY MOBRIS M. LEIGHTOX 



{Abstra<it) 



A map of northwestern Illinois will be presented which will show (1) the 

 distribution of the known occurrences of gumbotil, (2) old soils separating 

 the loess and the till, (3) weathered till beneath unweathered loess, and (4) 

 unweathered till beneath unweathered loess. Graphs will also be used to show 

 the depths of leaching found in the different drift areas of northwestern Illi- 

 nois and also in the lowan drift area of northeastern Iowa. The direction 

 from which the ice came and the resultant changes in drainage, involving the 

 cutting of the Mississippi River gorge at Cordova, will be dealt with. 



Presented in fnll extemporaneously. 



Brief remarks were made by Mr. Leverett. with reply by the author. 



F0S8ILIFER0LS LOEt^S BEXEATH TILTED GALEXA DOLOMITE AT THE 

 BORDER OF THE BELVIDERE LOBE. IX XORTHWESTERX ILLIXOIS 



BY MORRIS M. LEIGH TOX 



(Abstfact) 



During the past field season an exposure in Winnebago Countj*, Illinois, w^as 

 found which shows tilted Galena dolomite over fossiliferous loess. The fossils 

 of the loess are badly crushed, but four distinct species were found, indicating 

 a considerable fauna. Curator Frank C. Baker, of the University of Illinois 

 Museum, pronounces them of early Peorian aspect. The position of the Galena 

 dolomite is such as to indicate glacial ice-shove. The exposure is situated at 

 the border of the Belvidere lobe, which the author previously referred to the 

 early Wisconsin stage. 



Eead by title. 



