508 GEOLOGY OF CENTRAL WISCONSIN. 



with a heavy talus or "ancle," composed of great blocks of the quai-tzite that have 

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

 a somewhat regular shape imparted by the powerfal joints that everywhere 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 bluffr, are 

 quite narrow, being backed by deep ravines openmg 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 boOn mentioned. 



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

 scribed, the cUff on the north side bemg 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 tills cliif the heavy quartzite beds are seen on the strike, and present, therefore, an 

 appearance of horizontality when viewed from the vaUey below. At the mouth of the 

 vaUey, S. E. qr., Sec. 20, T. 11, R. 7 E, the northern cbfi' is of horizontal sandstone, 

 behind which the quartzite passes, whilht the south chff terminates in a sharp rocky 

 point known as the DevU'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 

 soutli side of the range, with Sauk Prauie in front, and the high bluff with its roches- 

 iiwntonees surfaces of quartzite behind; these surfaces rise in rude steps, wliich are 

 due to the gradual northern dip. 



N^ear the top of the sides of the ravine shown by the map on the southwest comer of 

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

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

 sides of the valley until we roach 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 quartzite ranges. This occurrence itself is not necessarily any such 

 mdioation, for the sandstone is found only at a high level, and may .herofore have been 

 introduced from the northward, quite mdependently of the valley of Devil's Lake, wliich 

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



This vaUey 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 be efficted by the agjncy of running water. Confirming 

 this view, we find, liigh up on the chfi' sides, within l-'iO ft.'et of the summit, remnants of 

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

 them many small pebbles and smootlied 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 cbift heaps that are now to be seen in it, and 

 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, whioli the deflectei 

 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 tliis is a 

 correct view, the river must have had a passage through the northern range also, an 1 

 this passage would be found m 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 ss a suggestion only. The Baraboo may be the stream ts 

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

 larger and more powerilol stream than now. Only ten miles above on its course t'l- 

 gorge through which it parses the northern rang? p esents no such proportions as se3 1 



