36 BULLETIN OF THE UNIVERSITY OF WISCONSIN 



direction for a distance of nearly thirty miles, and are 

 known as the north and south ranges of the Baraboo 

 Bluffs. In altitude they vary from a mere rise above 

 the surrounding country to a height of five and even six 

 hundred feet. 



The north range, which is not so prominent as the south 

 range, is joined to the latter at the eastern and western ex- 

 tremities, forming thus a canoe-shaped chain of bluffs, en- 

 closing within a depressed area three or four miles broad 

 at its widest part. Near the western end, where the 

 Baraboo River enters the area, and also near the eastern 

 end, where it emerges again, the north range is broken 

 down by deep gorges known respectively as the Upper and 

 the Lower Narrows. 



The rock material of the Baraboo Bluffs is mainly of 

 bedded quartzite, over whose upturned edges lie horizontal 

 beds of sandstone and conglomerate, capping and flanking 

 the ranges. Besides these sedimentary rocks there occurs 

 in the vicinity of the Lower Narrows a considerable area of 

 eruptive material. 



The geology of the sedimentary rocks ' has already been 

 quite well worked out. The quartzite, which belongs to 

 the Upper Huronian formation, is usually hard and 

 massive, but in a few places there occur beds and zones of 

 quartzite schists and slates. The dip of the quartzites is 

 always to the north, and varies from 15" at Devil's Lake 

 in the south range, to 60° at the Upper Narrows and 

 even 90"^ at the Lower Narrows in the north range. This 

 ever increasing dip from the south toward the north in- 

 dicates, as shown by the Wisconsin geologists,- that the 

 two ranges are the remnants of the north half of a great 

 anticlinal fold. The sandstone and conglomerate, as well 

 as a few small areas of limestone, all of which are of Up- 

 per Cambrian age, lie in horizontal beds capping the ranges. 



1 Correlation Papers — Archean and Algonkian, by C. R. Van Hise. Bulletin 86, U. S. 

 Geological Survej- ; pp. 105-107, 111, 140, 148. 



The Baraboo Quartzite Ranges, by E. D. Irving. Geol. of Wis., Vol. II; pp. 50G, 507. 



