THE ARCII^AN ROCKS. 433 



eases someiimes evidently results for the most pnvt from a direct disin- 

 tegration of tlie felspathic rocks in place, but sometimes also from a 

 disintegration of similar rocks in the drift. The descent of the re- 

 gion southward has caused the river valleys and smaller watercourses 

 to be cut deeply into the rocks, which are hence best exposed along 

 streams. As already said, however, exposures occur also somewhat 

 widely scattered away from the streams. Some large areas, as, for 

 instance, the country along the Fourth Principal Meridian, from 

 town 30 to town 42, are without rock exposures, the drift covering 

 being especially heavy. 



" By far the most common one of the crystalline rocks in this area 

 is gneiss; next in order of abundance are granitoid gneiss, granite, 

 syenite, hornblende rocks, chloritic schists, mica-schists, quartz-schists, 

 quartzite and felsitic rocks. In one small district on Black river in 

 Jackson county are large exposures of silico-ferruginoiis scliists (iron 

 ores), associated with silico-magnesian (talcose) schists. All of these 

 general kinds include many varieties, which are noted in the follow- 

 ing detailed descriptions. The granitoid and gneissoid kinds have 

 most commonly a moderately coarse character. 



The original bedded condition of the whole series is rendered suf- 

 ficiently evident, not only by a prevailing gneissoid and schistose 

 character, but also by the existence of distinct bedding planes 

 and lamination lines, which, though often obscured by cross-jointing, 

 especially in the granitoid kinds, can nevertheless, in general, be 

 readily made out. That the processes of metamorphism and disturb- 

 ance have been carried almost to their last extremes is shown by the 

 highly crystalline character of the rocks, the grading of the gneiss 

 into granite, the greatly contorted condition of the gneiss laminaa,' 

 and the close folding of the whole series. In some places, portions 

 of the arches are left; but in general erosion has removed or ob- 

 scured all the crowns, and has made of what must once have been a 

 lofty mountainous region, one in which the variations from a general 

 level are only those of insignificant ridges, and comparatively shallow, 

 eroded watercourses. 



Whilst the bedding of the whole series is thus evident, distinctly 

 intrusive granite occurs, its nature being indicated by the way in 

 which it joins and penetrates the bedded rocks. This extravasated 

 granite is usually of a pinkish to reddish color, often very bright 

 red, and occurs in very large masses. 



A tendency to weather characterizes most of the gneisses and other 



' Most beautifully exhibited on Black river, just below the crossing of the Green Bay 

 Eailrcad. 



