508 GEOLOGY OF CENTRAL WISCONSIN. 



with a heavy talus or "ancle," composed of great blocks of the quartzite that have 

 fallen from the cliffs above. These masses are often as much as 20 feet on a side, with 

 a somewhat regular shape imparted by the powerful joints that every where traverse the 

 quartzite, and cut it into blocks only needing to be slightly dislodged in order to fall 

 down the cliff. For the greater portion of their lengths both east and west blufft, are 

 quite narrow, being backed by deep ravines opening northward. The northern end of the 

 east bluff, especially, is a mere crest, having behind it one of the ancient sandstone- 

 lined ravines that have before been mentioned. 



In its east and west extension, the valley preserves the same characters as above de- 

 scribed, the cliff on the north side being the highest and boldest, and retaining for a 

 long distance the height it attains at the corner where the valley bends. Along the face 

 of this cliff the heavy quartzite beds are seen on the strike, and present, therefore, an 

 appearance of horizon tality when viewed from the valley below. At the mouth of the 

 valley, S. E. qr., Sec. 20, T. 11, R. 7 E, the northern cliff is of horizontal sandstone, 

 behind which the quartzite passes, whilst the south cliff terminates in a sharp rocky 

 point known as the Devil's Nose . From the summit of this cliff, a short distance west- 

 ward from the nose, is taken the view on Plate XV., the Frontispiece of this report. The 

 outlook is northwestward through the east and west part of the valley to the lake, be- 

 yond which the western cliff of the lake is seen. Doubling the nose, we are on the 

 south side of the range, with Sauk Prairie in front, and the high bluff with its roclies- 

 montonees surfaces of quartzita behind; these surfaces rise in rude steps, which are 

 due to the gradual northern dip. 



Near the top of the sides of the ravine shown by the map on the southwest corner of 

 the lake, horizontal sandstone and coarse conglomerate occur, the pebbles of the con- 

 glomerate coming from the quartzite against which it lies. Nowhere else along the 

 sides of the valloy until we reach its eastern end are any indications of its ever having 

 been filled with sandstone, and, consequently, of its equally great antiquity with other 

 ravines about the quarteite ranges. This occurrence itself is not necessarily any such 

 indication, for the sandstone is found only at a high level, and may therefore have been 

 introduced from the northward, quite independently of the valley of Devil's Lake, which 

 we are thus led to believe is of more recent origin than the Potsdam period. 



This valley has evidently been at some time the passage of a large stream. We can- 

 not suppose that it has been produced by any other process than that of erosion, and 

 such an erosion as could only b,3 effactecl by the agancy of running water. Confirming 

 this view, we find, high up on the cliff sides, within 150 feet of the summit, remnants of 

 large potholes, several feet in diameter, presenting smoothed surfaces, and having about 

 them many small psbbles and smoothed boulders which may have been engaged in the 

 work of then- formation. The large size of the valley suggests that it may have been 

 the passage of the Wisconsin river, which at the close of the Glacial period found its 

 ancient channel obstructed by the great drift heaps that are now to be seen in it, an:l 

 was forced to find its way eastward to the valley of the great river that for long ages 

 before the Glacial period drained the whole basin of the Wolf and Upper Fox through 

 the valley of the Lower Wisconsin to the Mississippi. This valley, which the deflected 

 river reached at Portage, and which it subsequently appropriated as its own, passes al- 

 together to the eastward of the eastern extremity of the quartzite ranges. If tin's is a 

 correct view, the river must have had a passage through the northern range also, an I 

 this passage would be found in the Lower Narrows, of the Baraboo, a much wider 

 channel than is needed by that small stream. This explanation of the origin of th^ 

 Devil's Lake valley is offered as a suggestion only. The Baraboo may be the stream t) 

 which the work should be allotted, but, if so, we must imagine it to have been a mu^'i 

 larger and more powerful stream than now. Only ten miles above on its course t'u 

 gorge through which it passes the northern rang3 presents no such proportions as se3.i 



