THE ARCHAEAN ROCKS. 505 



its friable and non-resistant nature. The country on top of the range is heavily timbered 

 presenting in this regard, as also in its almost universal heavy clay soil, a marked con- 

 trast with the lower country around. This clay soil has caused the making of many ex- 

 cellent farms on top of the range. It occurs alike on the quartzite and the high-level 

 sandstone. In the eastern extension of the bluffs it might be regarded as of glacial ori- 

 gin, but to the westward the glacial drift limit is reached about midway in the length 

 of the range, and some other origin must be sought. 



The northern range is much less pronounced than the southern. For about seven 

 miles west from the junction of the two, in Columbia county, it f orms a continuous ridge 

 some 300 to 400 feet in height, but generally much less than a mile in width. Further 

 west its height lessens for long distances, the Archaean rocks forming its core at -the 

 same time becoming covered by the overlying horizontal sandstones, through which 

 they appear here and there in small outcrops. Farther west still this range rises again, 

 and where it joins the cross ridge at its western extremity has become again bold, with 

 a height of 200 to 300 feet. Although thus indefinite in its middle portions, the higher 

 ground never entirely disappears along the line of the range, except at the three points 

 where the Baraboo river and one of its tributaries cut through in deep gorges. 



The depressed area within the circuit of the quartzite bluffs is, for the most part, 

 somewhat higher than the surrounding outside country, and towards its eastern and 

 western extremities rises rather rapidly up to the enclosing ridges. In Columbia county 

 much of the area between the ranges is as high as the northern range itself, and is un- 

 derlaid by a great thickness of sandstone, which fills in the canoe-shaped trough of the 

 uniting quartzite belts. At one time the rest of the valley between the ranges was 

 filled in a similar manner, and has since been partially recarved in the friable sandstone 

 which still forms its bottom. This valley is now traversed longitudinally by the Baraboo 

 river, vfhich enters and leaves it by deep gorges through the northern ridge, having a 

 fall between the gorges of about 70 feet. 



The rock constituting the great body of the Baraboo ranges is a qua,rtzite of a non- 

 granular, usually flaky, texture, and of a color from nearly white, through gray, pink, 

 and amethyst, to purplish-red and even brick-red, the gray and deep-red being the most 

 common, the white the least so. Very rarely a distinct granular texture is seen, some- 

 what more commonly a slight tendency in that direction. The quartzite is frequently 

 very distinctly laminated, the lines of lamination being contorted in a remarkable man- 

 ner, and marked by alternating light-colored and dark-colored lines. There is never 

 any cleavage parallel to the lamination lines. Next in abundance to the regular quartz- 

 ite, and merging into it, are heavy beds of a fine metamorphic conglomerate, usually of 

 a grayish to amethystine color, in which the matrix and pebbles are alike of quartzite, 

 and not always very well defined from one another. Forming thin layers between the 

 thick layers of quartzite, is in many places to be seen a peculiar greasy-surfaced quartz- 

 schist, the laminae of which are composed of quartzite like that of the regular quartzite 

 layers, seamed and covered on the surface with a soft, lilac to white, talc- like, mineral. 

 This slate or schist usually exhibits the true slaty or transverse cleavage. The soft 

 mineral pervading it- is suspected to be always, as it certainly is sometimes, aluminous 

 rather than magnesian. It occurs occasionally forming slaty layer? with but little 

 quartz admixture, and, in small seams, even entirely pure. It then has rather the 

 physical characters of a compacted clay, and this appearance is borne out by the analyses 

 given beyond, which show that the pure clay-like kinds are probably not distinct miner- 

 als, but rather a mixture of a clayey substance with fine silica. In both physical prop- 

 erties and chemical composition this material is closely allied to the pipestone of south- 

 west Minnesota, from which it differs only in color. 



Other quartz-schists of quite a different character have been observed forming the 

 lowest layers of the north quartzite range, both at the Lower Narrows of the Baraboo 



