30 < r K< >LOG Y OF J LLINOIS. 



sensed, and present an appearance exactly identical with those picked 

 out of the outcrop near the Illinois Central Railroad depot in Galena. 

 It will thus be seen, I think, that the evidences of the deposition of 

 loess deposits in this county are iucontestible. 



In the Fever river valley, within the city of Galena, a mile or two 

 above the city, and at several places between the city and its conflu- 

 ence with the Mississippi river, there are well denned river terraces of 

 modified or river drift. These are about twenty feet above ordinary 

 water mark in that stream. Similar traces were observed by Professor 

 WORTHEN at the mouth, and up the valley of the Small-pox creek; and 

 a broad, distinctly marked river terrace may be observed in the lower 

 part of the Mississippi bottom, extending down into Carroll county. 



Drift Proper. The productive lead field has been written down as '' a 

 driftless region ;" and to some extent this is true of that part of it 

 within Jo Daviess county. But in attempting' to account for this sup- 

 posed absence of the drift in the lead region, eminent geologists have 

 fallen into a controversy, or difference of opinion. 



WHITNEY contends that when the lead region was uplifted from the 

 Silurian seas, no subsequent submergence ever took place ; and that all 

 the changes which have since taken place on its surface, have been pro- 

 duced by agencies, such as we now see producing dynamical results 

 upon dry land. When the broadly extended drift forces whether 

 broad creeping and grinding glaciers, or broad water currents, or ice- 

 bergs and water acting together moved the drift on its south-west 

 course, according to this theory, the lead region rose as an island in the 

 midst of the moving forces, and the drift stream was divided thrown 

 to the east and west and united again after passing the obstruction. 

 Such being the case, the lead basin, supposed then to have been ele- 

 vated above the surrounding country, escaped the action of the drift 

 forces. During all this time, more peaceful geological causes are sup- 

 posed to have been at work over the uplifted island, whose action has 

 produced all the geological changes supposed to have, taken place. 

 Atmospheric and chemical agencies disintegrated the hard Silurian 

 rocks. The surface rocks changed slowly into the clays now overlying 

 the bed rocks, except so far as rains and winds may have transported 

 these clays and subjected them to a mixing process. This being true, 

 the superficial deposits of the driftless lead region are substantially in 

 S//H, at the very places where they were formed by the decay of the 

 parent rock. 



PERCIVAL believed that the high water shed, extending from the 

 mouth of the Wisconsin eastward, rose as a reef in the drift epoch 

 waters, and turned the drift to the west, through Iowa, and to the east, 

 round the lead region. This reef may have permitted a sheet of shallow 



