CIO GEOLOGY OF CENTRAL WISCONSIN. 



could ever have acted there. Flanking the north side of the quartz - 

 ite bluff at J^ecedah, in Juneau county, is a great bank of gravel and 

 rounded bowlders, but these are wholly of quartzite, derived from the 

 bluff itself, and must hence be regarded as the result of river or lake 

 action upon the quartzite. Clay and sand deposits occur in much of 

 Adams county, as, for instance, around Friendship, but are finely lam- 

 inated, and appear to be due to deposition from expanded streams or 

 lakes, being wholly without associated gravel. From southern to 

 northern Adams, the drift limit, as marked by the loose materials of 

 the surface, is for the most part directly along the edge of heavy mo- 

 rainic heaps, with numerous bowlders. 



Westward from Grand Rapids, the drift limit is not always so well 

 defined, but does not appear to be far from the line of the Green Bay 

 and Minnesota railroad, as far as the crossing of Black river. From 

 here it bends to the northeast, crossing the line of the West Wiscon- 

 sin road some twelve miles southeast of Eau Claire. 



The nature of the topography of the driftless area, everywhere 

 most patently the result of subaerial erosion exclusively, is even more 

 striking proof that it has never been invaded by the glacial forces 

 than is the absence of the drift material. Except in the level country 

 of Adams, Juneau, and eastern Jackson counties, it is everywhere a 

 region of narrow, ramifying valleys, and narrow, steep-sided, dividing 

 ridges, whose directions are towards every point of the compass, and 

 whose perfectly coinciding horizontal strata prove conclusively their 

 erosive origin. A glance at the map of Plate XXVI, on which are 

 accurately represented all but the very smallest streams, will serve to 

 give an idea of this feature of the driftless area. Each one of the 

 numerous streams shown has its own ravine, and the ravines are all 

 in direct proportion to the relative sizes of the streams in them. This 

 is well brought out by the colored geological maps of Areas D, E, G 

 and H, in the Atlas. Since the several strata lie nearly horizontal, 

 the colors representing them give really a close idea of the topography. 

 The two first named maps include portions of both drift-bearing and 

 driftless areas, and the different appearances of the geological outlines, 

 stream and marsh directions, etc., on the east and west sides of the 

 maps, are very instructive. It should be said that this difference is 

 due, also, partly, but not mainly, to a change which takes place mid- 

 way within the districts represented by these maps, from a nearly 

 perfect east and west horizontal! ty of the strata to a small, but grad- 

 ually increasing, eastward descent. In this connection, reference 

 should also be made to Mr. Strong's excellent contour maps of the 

 lead region. 



