BROWN AND REDWOOD COUNTIES. 571 



Kaolin.} 







channels and other exposures, this decomposition reaches in some places to 

 a depth of 20 or 30 feet, perhaps more. All grades of change may be found, 

 from ledges where only here and there a few spots have been attacked and 

 slightly decomposed, to portions where nearly every indication of the origi- 

 nal structure has been obliterated. 



Of these decomposed rocks on the Redwood river, Prof. Winchell wrote in the second 

 annual report of this survey: "At Redwood Falls the granite is overlain by the kaolin, which has 

 been mentioned, presenting, in connection with this substance, a very interesting series of ex- 

 posures, and suggesting very interesting questions both economical and scientific. About a mile 

 below the village, on the left bank of the river, is a conspicuous white bluff (probably that seen by 

 Keating, and pronounced white sandstone), composed of white kaolin clay. Near the top of this 

 bluff, where the rains wash it, it is silvery white, and that color is spread over much of the lower 

 portions, though the mass of the lower part is more stained with iron, having also a dull greenish 

 tinge. The white glossy coating which appears like the result of washings by rains, is spread over 

 the perpendicular sides. On breaking off this glossy coating, which is sometimes half an inch 

 thick, the mass appears indistinctly bedded horizontally, but contains hard lumps and irony 

 deposits. Further down, the iron becomes more frequent, and gritty particles like quartz impede 

 the edge of a knife. The bedding is also lost, and the closest inspection reveals no bedding. Yet 

 there is, even then, a sloping striation or arrangement of lines visible in some places on the fresh 

 surface, that corresponds in direction with the direction of the principal cleavage plane of the 

 talcose and quartzitic slate already described. In other places this arrangement is not seen, but 

 the mass crumbles out in angular pieces which are superficially stained with iron. The profile of 

 the bluff here presents a singular isolated knob or buttress that rises boldly from the very river, 

 connected with the main bank by a narrow edge along which a man cannot walk with safety. 

 On either side of this bold promontory are retreating angles in the bluff along which a descent 

 can be made. A careful inspection of these ravines and of the adjoining bluffs affords indubitable 

 proof that this material, white and impalpable as it is, results from a change in the underlying 

 granitic rocks. 



"Just above this point is another exposure. It here supplies what is locally known as the 

 'paint rock', from an enterprise started several years ago in the manufacture of mineral paint from 

 this material. The decomposed granite here has very much the same appearance as the kaolin 

 at Birch Cooley, but contains more quartz, and is more stained with iron. It has a greenish color 

 but within might be blue. It passes upward into the greenish, and then white, kaolin clay already 

 described, but it stands out in a crumbling, rusty buttress, exposed to the weather, and has 

 quartzitic grains and concretions, iron-coated, and often an impure iron ore in considerable quan- 

 tities. It shows silvery or shining talcose flakes, the same as seen in the so-called building rock, 

 a short distance below the mill of Birum brothers. 



"A short distance above this, nearly opposite Redwood Falls, is situated the rock which was 

 quarried for the manufacture of paint. This has in every respect the same character and compo- 

 sition as that last described. It consists of a perpendicular bluff or point, standing out from 

 a lower fcilus that rises about 75 feet above the river, to the hight of 75 feet more. On the top of 

 this is the drift-clay hardpan, covered by four or five feet of sand and gravel, the whole bluff being 

 about 150 feet above the river. This bold bluff, or promontory, stands between re-entrant angles 

 its face falling down sheer thirty or forty feet. There is here visible an irregular slaty or cleav- 

 age structure in the rock, that at a distance has the appearance of dip toward the S. E. 30. This 

 also contains quartz veins and deposits, accompanied by iron, in some places too abundantly to 

 allow of being cut with a knife, though very much of it can be easily shaped with a knife. It 

 shows 'slickensides,' or surfaces that seem to have been rubbed violently against each other, caus- 

 ing a scratched and smoothed appearance, even within the body of the bluff. These surfaces are 

 concave or curving, like putty hardened after being pressed through a crevice." 



Before the extensive denudation of the glacial period, it is probable that all the granite and 

 gneiss of this region were covered by a similarly decayed surface. Upon the areas where de- 

 composed rocks still exist, the glacial plowing was shallower than elsewhere. These kaolinized 



