GEOLOGY OF CENTRAL WISCONSIN. 



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hill this character is less marked, and the rock (1253) is a dark 

 reddish-purple quartzite with a distinct tendency to a granular 

 texture, the individual grains being vitreous and translucent, 

 but the rock as a whole having a dull, opaque appearance. The 

 bedding of the quartzite is not everywhere very plain. Towa rds 

 the north the layers appear to conform to the directions noticed 

 in the overlying porphyry, but further southward the inclination 

 is much steeper, and on the south slope, near the end of the 

 ridge, beautifiuUy ripple-marked vertical surfaces, are seen. In- 

 terstratified with the quartzite in places are some greasy-sur- 

 faced scliistose layers. At the foot of the hill, near Mrs. Gar- 

 rison's house, the low est member of the series is s^en in a pecu- 

 har white to straw-colored quartz-schist or slate (1284). This 

 slate occurs in regular smooth-faced, brown-tinted, layers, ^^th 

 inch to 3 or 4 inches in thickness, and has a fine granular tex- 

 ture, the grains being of more or less angular quartz. Sur- 

 roundhig the grains and pervading the mass is a fine white 

 pulverulent matrix, which renders the rock soft, and has u, 

 highly argillaceous odor when breathed upon. Only about 15 to 

 20 feet are exposed. The northward dip is very plam, the 

 edges of the layers in places being much bent out of the true 

 inchnation, which, as seen in the old shaft near by, is as much 

 as f30° to 70°. The whole thickness of the metamorjjhio rocks 

 represented in this section is not far short of 5,000 feet. 



A short distance westward, and a few feet above the quartz- 

 schist just described, horizontal sandstone is quarried. Further 

 up the bluff, this is succeeded by a great thickness, probably 

 a hundred feet, of a horizontally bedded, coarse bowlder-con- 

 glomerate, the bowlders chiefly of red quartzite from the rocks 

 near by, and the matnx usually a loose friable sand. The con- 

 glomerate rises nearly, or quite, to the summit of the ridge. 



The east bluff of the Narrows does not present so fine a sec- 

 tion as the one just described; the exposures are, however, very 

 large. At the south point of the cliff', the elevation ia 310 feet 

 above the Baraboo, and the rock a very compact, rod-tinged, 

 slightly vitreous quartzite. Near the middle of the cliff, a very 

 steep ravine indents its face. On the south side, and around the 

 head of the ravme, are horizontal ledges of a conglomerate of 

 quartzite pebbles up to. 6 inches in diameter, for the most part 

 without matrix. What matrix is present appears in many 

 places to be almost as much of a quartzite as the pebbles them- 

 selves, though in others it is sandy and friable. On the north 

 side of the ravine, semi-translucent, amethystine quai-tzite is 

 seen, unconcealed by conglomerate. Further nortliward, the 

 steep N. 70° dip of the quartzite is very plain, the dip surfaces 

 being often laid bare for a great distance, and giving a very 

 steep slope to the north side of the ridge. The east cliff' of the 

 Narrows does not extend so far north as that on the wesf . 



"W^est from the Narrows, for about two miles, the north 

 face of the range trends north of west, continuing to show all 

 along beds of quartz- poi-phyry. Since the strike throughout is E. 

 W., the existence of a very much broader belt of porphyry than 



