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degrees. At one place at Granite Falls the rock dips to the north for some distance. The red and grey colors are variously mingled, without any apparent law of association or alternation. Although the patches of more massive and typical granite are suitable for a fine building material, they still show the same dip toward the S.E., and are distinctly bedded throughout. These hard knobs rise from ten to twenty feet above the general level of the other granite, and show various effects of running water.

The trap dykes, the direction of which is shown by the adjoined diagram, occur in the river bottoms, about a mile above Granite Falls.

[blocks in formation]

There are sudden changes in the rock from real granite to hornblendic schist. These occur irregularly. A change like this gives rise to the waterfall near the flouring mill of Hon. Henry Hill, the fall being due to the greater resistance of the harder rock. The trap dykes above mentioned also cause rapids and waterfalls where they cross the river.

Between Granite Falls and Montevideo, at the mouth of the Chippewa river, the granite occasionally appears in the river bottoms. It was noticed at a point six miles below Montevideo, on the north side. The bedding, supposed to be due to original sedimentation, still dips to the east. It appears sometimes to stand nearly vertical. At this place occurs a belt or bed of hornblendic schist.

At two miles below Montevideo, is a conspicuous outcrop of compact hard granite, of a red color, lying mainly on the north side of the river, in the bottoms. This has the same dip, viz., 30 or 35 degrees to the southeast. The beds here regarded as representing dip, and at other points mentioned, should be further described. They are in thickness to 2 or three inches, or they seem sometimes to be a foot or two. When weathered they appear thiner, and the granite then sometimes presents a slaty structure, the edges standing out sharply at the angle of dip. At Minnesota Falls,

and from there to Granite Falls, these beds are so micaceous as to make what has been termed a schistose granite, the whole mass becoming easily disrupted by frost and water, and then turfed over. But at this place the beds are closely compacted, and the whole is almost massive. The thickness of the bedding can easily be seen, however, in the occasional thin sheets that part from the knobs, or in the striations that mark the faces of the waterworn, bald knobs. Although these knobs rise at irregular intervals, and are variously situated with reference to each other, having sloughs between them, yet they are arranged somewhat in succession in one direction, making rows or almost sometimes continuous ridges, running parallel in the direction of the strike, N.E. and S. W., which of themselves indicate a system of bedding. On a weathered cross-section of the bedding, the marks of striation or sedimentation often show a wavy arrangement, or distorted parallelism, and sometimes they vanish and widen alternately. The dip measured in one place is here 58°, 10° east of south. At another point, very near the last, it is 85° in the same direction. This granite has the color and apparent composition of that seen below Fort Ridgely.

This granite shows occasionally a knob of hornblendic schist, rising among the granite mounds, having very much the form, dip and bedding of the granite.

There is also occasionally a mound or dyke of trap, or greenstone, split into shapeless blocks under the weather, the planes of division running in various directions. These have no bedding, nor dip, but are very heavy, and uniformly of a dark green color. They do not disturb the uniformity of dip in the granite.

The following diagram will exhibit some of the features of the granite as exposed two miles below Montevideo :

[merged small][subsumed][subsumed][merged small][graphic][subsumed][subsumed]

The change in the direction of dip in the granite here sketched is rather less sudden than here represented. The seam,or joint, marking the point of contact of the beds dipping in different directions, is very much covered with turf, and the manner of union cannot be ascertained definitely, but on the face of the bluff (strike) there is no apparent disturbance or irregularity.

A belt or wedge-shaped, lenticular mass of hornblendic schist occurs in the granite here described, on the land of Mrs. E. A. Hull, having more easterly dip, and running N.W. and S.E. It is 20 rods long, and from 20 ft. to 6 rods wide. Its dimensions and form cannot be fully and exactly seen. It appears in low knobs much like the granite, and the intervals of non-exposure are grassy.

Mr. L. R. Moyer, county surveyor of Chippewa county, reports granite on the prairie, three miles east of Montevideo, and in the Minnesota bottoms, a mile above Montevideo.

Near the lower end of Lac-qui-parle lake, granite appears on both sides of the lake. It is usually inaccessible from

Strike

the prevalence of water; but in the dry months of the year it can be reached on the north side without any trouble, except from tall grass and bushes. There are three or four small bare spots on the south shore that can be seen, and three or four others that rise up in the midst of the lake. Two of these spots of bare rock also occur on the north side, near the foot of the lake. This rock, so far as can be seen on the north side, shows very much the same composition as further down the river. It contains quartz, mica and flesh-colored feldspar, with patches and veins of quartz, some of which are mingled with porphyritic feldspar. The exposed surfaces are annually submerged, or nearly so, and do not exhibit very plainly such markings as indicate sedimentation or dip. There seems to be an indistinct arrangement of the mica scales, so as to give the rock a schistose structure, but this, although generally running N.E. and S.W., does not have that direction invariably, and does not at all represent the lamination or bedding seen below and already described. In only one small area can there be seen what looks like the same bedding, and there it is but six inches in thickness, the beds being one or two or three inches, with a dip of 75° toward the S.E. Jointing planes divide the whole mass into blocks and rhombs, four or five or six feet in thickness. There is a considerable low land about the lake, much of which is flooded at the wet season of the year, but it is stony and bushy, and has the appearance of rock in a great many places near the surface. Such appearances are seen the whole length of the lake, and especially on the north side. About three miles above the foot of the lake, rock can be seen on the south side at two points, rising plainly above the general level of the bottoms, and ascending in the slope from the prairie. Such exposures continue to near the head of the little lake on T. 120, R. 44, where granite appears in several places on the south side of the river.

Further up the river, near where it enters T. 120, R. 44, may be seen a large exposure of coarse granite. The crystals of feldspar are large and flesh colored, or red. Yet the granite also varies to a lighter color, in which the feldspar is nearly white. It shows, in the latter case, a perpendicular jointing, the planes being one or two or three inches apart. The whole exposure consists of bare, massive, rounded knobs, cut into angular rhomboidal blocks, by jointing planes, but in no place showing the dip seen lower down the Minnesota river.

Granite also outcrops about three quarters of a mile above Mr. F. Frankhouse's, on the south side of the river, two miles above the last.

Red granite also appears about a mile further up, in the river bottoms, near Mr. W. Movius' house, presenting an irregular exterior, showing no dip, although there are here also conspicuous jointing planes. This is about three-fourths of a mile above the mouth of the Yellow Banks creek. Opposite Mr. Movius', on the south side, in the bottoms, may be seen another similar granite mound. At three miles below the foot of Big Stone Lake, there is a tumultuous outcrop of red granite, extending to the lake on both sides of the river. This shows planed and striated surfaces on a grand scale. These marks have a N.W. and S.E. direction (corrected for variation), or that, in general, of the Minnesota valley. The whole rock, including the upper surfaces and the sides of the mounds, is planed off. The best exhibition of these markings is seen on the northwestern slopes, in which direction there is a system of jointing planes, dividing the granite into blocks that have at first sight a strong semblance of dip, the masses breaking off more nearly at right angles on the southeast side. This is a coarse, red granite, with large crystals of feldspar. The following diagram illustrates the effect of the jointing in the rock, acted upon by glacial forces from the northwest.

Jointing and Glaciation at Big Stone Lake.

[graphic][subsumed]

Above the foot of Big Stone lake there is no known outcrop of granite throughout its extent. Cretaceous rocks constitute the only outcrops. These are seen sometimes in the little creeks that enter it, and are outlined as terraces on its banks.

The examiners of the land of the Winona and St. Peter R. R. report granite in situ, on the prairie T. 113, R. 43, Sec. 17, and T. 113, R. 39, Sec. 29.

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