oiH GEOLOGY OF CENTRAL WISCONSIN. 



II. Special Descriptions of the Several Areas. 

 THE BAKABOO QUARTZITE KANGES. 



The Baraboo quarfczite ranges occupy much the largest extent of territory, and are 

 at the same time much the most striking and most important as influencing the to- 

 pography of the state, of any of the isolated Archaean areas that occur within the region 

 of the Silurian rocks. Their bold character, and the dissimilarity between their rocks 

 and those of the country around, have drawn to them the attention of previous State 

 Geologists, as weh 1 as of other scientific men. Percival 1 regarded the quartzitcs com- 

 posing the ranges as resulting from a metamorphism of the Potsdam sandstone of the 

 surrounding region. Hall 2 refers them correctly to the Archaean, making them Huro- 

 rian, but his detailed examinations were not published. Alexander Winchell 3 calls them 

 "Lower Potsdam," on the evidence of some fossils belonging to the middle Potsdam, 

 and found in the sandstone lying against the quartzite. This he regards as proving the 

 " Lower Potsdam " age of the quartzite, losing sight of the fact that the latter is uncon- 

 formable with the sandstone, and projects upwards into the horizon, not only of the 

 middle Potsdam, but even far above into that of the St. Peters. The Archaean age of 

 the quartzite was first definitely proved by the writer in 1872, 4 and this conclusion has 

 since been abundantly confirmed by the work of other geologists, 5 and also by his own 

 further researches in the region. 



The Baraboo Bluffs constitute two east and west ranges extending some 25 miles in 

 length through the towns of Caledonia, in Columbia county, and Greenfield, Merrimack, 

 Sumpter, Baraboo, Honey Creek, Freedom, Excelsior and Westfield, in Sank county. 

 The southern one of the ranges is much the bolder and more continuous, and the two 

 are not exactly parallel, but diverge as they are traced westward. At their eastern ends, 

 in Columbia county, they unite in a bold point, rising abruptly from the low ground of 

 the Wisconsin river, here at the easternmost point of the great bend which the quartzite 

 ranges compel it to take. Tracing them westward, we find the two ridges, about mid- 

 way in their lengths, some four miles apart, and at their western ends a mile or so more 

 than this; Here a bold, nearly north and south, cross-ridge, also with a quartzite core, 

 unites the two, thus finishing an entire cordon of bluffs around a depressed interior. All 

 around the outside of this circuit of hills, except beyond the western cross-ridge, the 

 country is comparatively low, and often quite level, so that the ridges rise very boldly, 

 forming, for a non-mountainous country, quite a striking feature of the landscape. 



The southern quartzite range is broken down in only one place, the gorge in which 

 lies the Devil's Lake, and, as seen from the low ground of the Wisconsin river on the 

 south, presents a continuous, wavy crest, often with large areas of bare rock, and with 

 elevations of from -500 to 700 feet above the river, and of 700 to 900 feet above Lake 

 Michigan. Its higher portions have a width of from one to four miles, the outline being 

 quite irregular on account of the deep and very anciently eroded valleys that indent its 

 sides. The great antiquity of these vaUeys is evinced by their showing on their sides 

 and bottoms layers of horizontal sandstone clinging to the underlying quartzite. The 

 sandstone has evidently been deposited in valleys which were originally formed long 

 before its deposition, and have been carved out anew in the same places, on account of 



i "Annual Report of the Geological Survey of Wisconsin," 1836, p, 101. 



Geology of Wisconsin, 1862. 



8 American Journal of Science II, vol. xxxvii, p. 226. 



4 Am. Journal of Science, Feb., 1872. 



* See J. H. Eaton " On the .Relations of the Sandstones, Conglomerate and Limestone, of Sank 

 county to each other and to the Azoic," Am. J. Sci. Ill, vol. V, p. 144, and T. C. Chamberlin on the 

 " Methods of Upheaval of the Baraboo Ranges," Wis. Acad. Sci.. vol. IT. 



