612 GEOLOGY OF CENTRAL WISCONSIN". 



The surface features of the drift-lbearing regions, so far as they 

 are independendent of the rock}^ formations beneath, are in strong 

 contrast with those of the driftless area. There is an almost entire 

 absence of the narrow ridge-and-valley topography, or of very steep- 

 sided valleys generally, the contours being everywhere more flowing. 

 The difference is evidently due both to a different method of erosion 

 and to the obliteration of abrupt changes of level by heavy deposi- 

 tions of drift materials Another marked difference is noticed in the 

 entire absence, east of the drift limit, of the fragile castellated out- 

 liers that are found further west. Outliers do occur, though not 

 abundantly, but are thick and of rounded contour, and more com- 

 monly of limestone. Still another contrast is presented in the linear, 

 and for considerable areas parallel, arrangement of the ridge, valley, 

 marsh, and stream directions, and also of the outlines of the areas oc- 

 cupied by the several formations, as compared with the ramifying 

 arrangement of the driftless region. To these features of the drift- 

 bearing districts are tp be added the peculiar appearance due to round- 

 ed hills and winding ridges of jDebblcs and sand, the abundance of 

 circular and serpentine depressions without outlet, and often occupied 

 by lakes of considerable size, and the omnipresent surface erratics — 

 all of which receive especial attention below. 



The features thus enumerated are especially to be observed in that 

 part of the state which lies east of the eastern boundary of the drift- 

 less area, the region lying immediately north of its northern bound- 

 ary, though showing in parts considerable quantities of drift material, 

 having apparently not been subjected to so great glaciation. In much 

 of the latter region the drift appears to be quite insignificant, and all 

 surface irregularities as purely the result of subaerial agencies as iu 

 the driftless region itself. This is quite evident along both sides of 

 the valley of the "Wisconsin from Stevens Point to tlie north line of 

 the district, and along the valleys of its principal western tributaries. 

 All along the line of the Wisconsin Yalley Kailroad, between Knowl- 

 ton and Grand Kapids, wherever the least cutting is made the rock 

 is laid bare. Farther west, on the divide between the Yellow and 

 Black rivers, in Clark and western "Wood counties, there is a consid- 

 erable thickness of drift material, which, however, presents none of 

 the heaped up appearance characteristic' of the more eastern drift- 

 bearing regions. 



The linear topography above mentioned is generally found best 

 marked in the regions east of the belt along which the drift materials have 

 their most marked morainic development. As shown hereafter, this 

 belt lies usually not far east from the western limit of the drift region. 



