462 



GEOLOGY OF CENTRAL WISCONSIN 



FIG. 1. 



the Atlas, \vliich give the boundary, for the region examined by the 

 writer, with as great accuracy as present knowledge will permit. 



The imconformability between the tilted crystalline rocks and the 

 horizontal sandstones is frequently to be observed along'the boundary 

 line between the areas of the two formations, and especially where 



the streams have cut 

 through the sand- 

 stones into the un- 

 derlying Archoean 



/=~l "^lL__ ^sllr^J In a number of places, 



f jr. 4f=____^3>^^^-_-'-- S ^=^__,___ *^7 as to which details 



are given in sub- 

 sequent pages, the 

 sxact junction of the 

 two formations can 

 be seen. In one 

 place on Black river 

 it is even possible to 

 obtain hand speci- 

 mens showing both 

 formations, and their 

 respective bedding 

 and lamination lines. 



SKETCH OF A SPECIMEN FROM NBAS BLACK RIVER FALLS, SHOW- 1* ig. 1 IS taken Il'Oin. 



ING THE EXACT JUNCTION OF THE POTSDAM SANDSTONE AND AR- 



. , ., . . * > one 



CHJEAN SCHISTS ; half the original size. 



o f fllP^P 



specmens. 

 The general topographical features of the crystalline rock dis- 



trict have already been indicated. It is an elevated area with an 

 altitude of from 500 to 900 feet, and highest on the north. In gen- 

 eral, it may be said to have a surface of gradual, though considerable, 

 changes in elevation. Looked at more minutely, however, the surface 

 is observed to be broken up frequently by low and narrow, but quite 

 steep, ridges, often with rock exposures at top. The whole region is 

 densely timbered, chiefly by pine. These pine trees, on account oi! 

 the small depth of their roots, are easily and frequently prostrated by 

 the wind, often over many square miles at once. Such windfalls, 

 when burnt over and grown up with a small second growth, combine 

 with the steep rocky ridges and the numerous small intervening 

 marshes, to render traveling in this region to the last degree difficult. 

 On the higher swells of the country, however, the pine is often re- 

 placed by hard wood, maple especially. In such parts, traveling is 

 easier, and excellent farms are obtained by clearing. The soil in these 



