428 GEOLOGY OF CENRTAL WISCONSIN. 



caused by divergence northward of the southern range, the northern 

 retaining its E. W. direction, is a bold, sharp point, rising abruptly 

 400 feet above the level valley of the Wisconsin. From this point 

 westward the southern range is a continuous ridge of 400 to 700 feet 

 elevation above the low ground on the south, and 600 to 900 feet 

 above Lake Michigan, always bold on both sides, often precipitous, 

 and rising at top into long rounded swells, which not infrequently 

 show the bare, purplish, quartz rocks. The wide, level prairie lying 

 south of the middle portion of this range, known as Sank Prairie, 

 makes it stand out all the more boldly. It is not, however, only near 

 by that this range is noticeable. It is seen from elevated points forty 

 miles to the north, where its rounded contours distinguish it from the 

 horizontal rock elevations seen on each side of it. Even from points 

 around Madison which has between it and the Baraboo Bluffs a 

 high limestone divide by the aid of a telescope, their rounded 

 contours can be distinguished through low places in the divide. 

 At their western ends the two quartzite ranges are a number of 

 miles apart, but are joined by a cross ridge of nearly the same alti- 

 tude, which has probably a quartzite core throughout. Except, how- 

 ever, over a large rounded elevation about midway in its length, and in 

 other places at its ends, this cross ridge shows only sandstone as the 

 surface rock. On the east the cross ridge descends rapidly to the 

 level of the Baraboo valley. On the west, the high ground descends 

 only gradually, and soon showing the Lower Magnesian limestone as 

 the surface formation, continues many miles westward. 



A remarkable feature of all of the paleozoic portion of central 

 Wisconsin is the occurrence of isolated ridges and peaks, ris- 

 ing from 100 to 300 feet abruptly, and often precipitously, from 

 the low ground around them, having an area on top of from a frac- 

 tion of an acre to a square mile, and composed of horizontally strati- 

 fied sandstone, or of sandstone capped with limestone. Such outlying 

 bluffs lie all along the face of the high limestone country of Columbia 

 and Dane counties, and are generally there capped by the same lime- 

 stone that forms the elevated land, of which they are themselves frag- 

 ments. Others again, and these are nearly all entirely of sandstone, 

 occur scattered widely over the central plain of Adams and Ju- 

 neau counties, often covering but a small area, and showing bare rock 

 from the base to the summit, which not infrequently is worn into 

 jagged pinnacles and towers. 



The following tables give the altitudes of numerous points through- 

 out the district, referred to Lake Michigan as zero. The railroad ele- 

 vations were furnished me by the late Dr. I. A. Lapham, who ob- 



