YELLOW MEDICINE, LYON AND LINCOLN COUNTIES. 597 



Eozoic rocks.] 







miles above Granite Falls, near the mouth of Stony run. Along this distance they are principally 

 on the southwest side of the river. In the N. E. } of section 24, Stony Run, the strike for an 

 eighth of a mile is S. 80 E., the dip being 75 N. 10 E. Generally, however, the strike is nearly 

 N. E. to S. W., the dip being southeasterly. In the northwest edge of Granite Falls, the dip is 

 60 S. E., but more commonly it ranges between 25 and 40. In a few places at Granite Falls 

 the dip is toward the northeast or north. At Minnesota Falls it was noted in one place to be 

 58 S. 10 E., and near by 85 in the same direction. These are exceptions, while the prevailing 

 inclination is toward the southeast. The strata are reddish or gray gneiss, frequently so disin- 

 tegrated by the weather that its outcrops have become turfed, varying occasionally to more en- 

 during gray and red granite. These rocks also sometimes include trap dikes, of massive, very 

 heavy, dark green rock, as at the rapids, recently used for manufacturing, one mile above Granite 

 Falls, where two dikes, respectively twenty and forty-eight feet wide, occur fii'ty-four feet apart, 

 their course being N. E. to S. W., conformable with the strike of the rocks. Elsewhere the gneiss 

 may include a bed or lenticular mass of hornblende schist, as is seen at the east end of Granite 

 Falls bridge and dam. Marks of water-wearing occur on these ledges in the vicinity of Granite 

 Falls to a hight of 20 or 30 feet above the river. Gray syenite, probably valuable for building and 

 ornamental purposes, occurs about a half mile south of Minnesota Falls. A large specimen of it, 

 elegantly polished, was shown me by Mr. Park Worden of this place. It is composed of white 

 quartz and black hornblende, in nearly equal parts, somewhat schistose as to the direction of its 

 grains. The trap dikes, hornblende schist, syenite and granites, are together but a small portion 

 of these rocks, which are mainly gneiss. Its outcrops from Granite Falls to one mile below Min- 

 nesota Falls are very prominent, rising in irregular and picturesque confusion throughout the 

 entire valley, nearly two miles wide. Lower ledges continue less frequently for a mile or two 

 beyond these. The next outcrops noted, also consisting principally of gneiss, are six miles down 

 the river, beginning in section 12, Sioux Agency, and extending eastward into Swede's Forest, 

 Redwood county. 



In Echo, the most southeast township of Yellow Medicine county, several outcrops of these 

 rocks occur from a half mile to one mile southwesterly from the lake of the Woods, being about 

 ten miles southwest from the Minnesota river. On land of Samuel Mathes, in the N. E. J of 

 section 32, they appear in three considerable ledges, besides other small exposures. The largest 

 of these ledges extends some eight rods from southeast to northwest, is three rods wide, and 

 rises four or flve feet above the general surface. It is mainly a reddish, compact gneiss, much 

 contorted. At its northwest end the dip of its lamination is 60 N. AV.; elsewhere the dip varies 

 somewhat, and is mostly obscure. In its north part this gneiss encloses a mass of dark, nearly 

 black mica schist, fifteen feet long and two feet thick, its length being in the same direction with 

 the lamination of the gneiss. This included mass is bounded by sharply defined lines. Its 

 southwest end tapers to a point, but at the other end it is abruptly truncated by an elsewhere 

 obscurely bounded vein of coarse feldspathic granite. Ten feet farther east is a second mass of 

 this dark micaceous rock, of irregular but well-marked outlines, about three feet long and one 

 foot wide, surrounded by coarse feldspathic granite and cut by a vein of the same, from one- 

 fourth of an inch to one inch wide. Similar very coarse granite also forms the southeast end of 

 this rock-outcrop, gradually changing to the gneiss which makes up the greater part of this ledge. 

 Thin veins of white quartz are seen here in a few places. About six and twelve rods northwest- 

 erly from the foregoing are two other exposures of gneiss, the northern one having a length of 

 about fifty feet, and a hight of five feet. At its north end the dip is 80 N. N. W. Other low 

 outcrops of small extent are found at a short distance eastward, on the N. W. J of section 33, 

 and at about a half mile to the northwest, near the center of section 29. 



Seven miles west from these rock-exposures, and at a distance of about fourteen miles 

 southwest from the Minnesota river, nearly on the line between sections 29 and 30, Posen, an 

 outcrop of reddish granite covers an area about ten rods long and eight rods wide, rising five to 

 fifteen feet above the adjoining land. It lies in a depression at the east side of a slough, and the 

 top of the ledge is slightly lower than the average hight of this region. This granite is mostly 

 medium-graineJ, but in some places of small extent, especially in its south part, it is very coarse 

 and principally made up of feldspar crystals, three or four inches long. It contains here and 

 there short quartz veins from two to six or eight inches wide. 



