SUEFACE RELIEFS. 427 



southward, forming a continuous river with the Wisconsin below 

 Portage. This former drainage southward has been suggested by 

 other writers, but most clearly by Geu. G. K. Warren, in his recent 

 report on the Fox and Wisconsin rivers, in which he shows that the 

 lower Fox, through which the entire basin of the upper Fox and 

 Wolf now outlets, is a modern channel, induced to form by a lower 

 position of the continent to the northward than it formerly had. The 

 real identity of the valleys of the upper Fox and lower Wisconsin, 

 now shown, seems to be a convincing proof of the theory. Moreover, 

 in subsequent pages it is shown that the upper Wisconsin has also 

 undergone a change of course, having at one time passed through the 

 Baraboo quartzite ranges, in the gorge now partly occupied by 

 Devil's Lake, and reached the valley of the lower Wisconsin in the 

 region of Sauk Prairie, more than 20 miles below the point at which 

 the Fox and Wisconsin now approach each other. It is shown that 

 this condition held until the Glacial Period, when, the gorge through 

 the quartzite ranges becoming choked with drift, the Wisconsin was 

 forced to find itself a new passage around the eastern point of those 

 ranges. But this passage around the point of the quartzite i-anges, 

 and as far southwest as the former junction of the upper and lower 

 Wisconsin, is just as ancient and as deeply eroded as the channel 

 of the lower Wisconsin itself. It follows that even when the upper 

 Wisconsin had its former course, there was still a great river occupy- 

 ing the valley immediately below Portage, and this could only have 

 come from the region of the Wolf and upper Fox. 



Of the subordinate dividing ridges we need only mention here the 

 quartzite ranges known as the " Baraboo Bluffs;" all others will be 

 described in the chapters on local geology. The Baraboo ranges, 

 however, constitute so striking a feature in the topography of the 

 central palceozoic portion of the state, and present so marked a con- 

 trast in direction and outlines to all other relief-forms south of the 

 main region of crystalline rocks, that they deserve especial mention. 

 They are two bold east and west ridges — the southern miich the bold- 

 er and more continuous of the two — extending through Sauk and 

 eastern Columbia county for twenty miles, and lying within the great 

 bend of the Wisconsin river. Their cores and summits, in some 

 places their entire slopes, are composed of tilted beds of quartzite, 

 metamorphic conglomerate, and porphyry, whilst their flanks are for the 

 most part made up of beds of horizontal sandstone, which, in lower 

 places, sometimes surmounts and conceals the more ancient rocks. 

 On the east and west the two ranges join, and thus nearly completely 

 surround the lower ground between them. The eastern junction, 



