which fills the interstices within the mass and between the grains of quartz and the crystals of feldspar, that seems to be generally redder than the distinct quartz or feldspar portions. Yet that loose and more finely pulverized part seems to be made up entirely of quartz, appearing, on close examination, to have the light color and distinct fracture of glassy quartz, the red color vanishing from sight. The color seems to be located very largely in the cement, as in the red quartzite at New Ulm, suggesting the query whether this may not be more highly metamorphic sandstone. In a deep fracture, however, the red color is much less observable, being replaced by a gray, the feldspar grains becoming more evident, and the whole rock appearing much like the St. Cloud granite.

Above Fort Ridgely, by following the only passable road, a number of granite outcrops were not seen. At a point two miles below the Lower Agency, T. 112, R. 34, Sec. 10, Mr. Wm. H. Post lives on the bottoms, near the mouth of a little creek coming in from the north. From him the following statements of granite in the bottoms above Fort Ridgely were derived. It outcrops much more frequently on the south side than on the north side of the river. Throughout the whole distance to the fort (10 miles) occasional mounds of bare granite rise up in the bottom land. But these exposures are often quite small and at some distance from the river. At Marshner's Carding Factory, seven miles above the fort, are a number of granite knobs, in the vicinity of a lake situated in the bottoms. Half a mile further up is another exposure, but more or less connected, by smaller exposures, with that at Marshner's. The next principal outcrop between Fort Ridgely and Mr. Post's, is on the south side of the river, and is visible from his house. It shows a conspicuous bared spot, with some timber, rising in one place nearly as high as the enclosing bluffs, but not effecting the general level of the prairie, unless it be in causing, as has been observed in one or two other places, a knobby or rolling tendency in the prairie surface, with gravel and boulders strewn over the surface of the knolls. One very prominent rock rises nearly forty teet above the general level, cone-like, and can be ascended only on one side. It bears a few cedars.

At Mr. Post's, granite outcrops occur at two places in the bottoms. These rise but few feet above the general level. This granite has a strong resemblance to that at La From boise's. It contains but little mica, and the feldspar is flesh-colored. The color here penetrates the feldspar crys

tals. In some places, however, the mica is more abundant, and the feldspar is less red.

Birch Coolie Creek joins the Minnesota in Sec. 5, T. 112, R. 34. The sides of this ravine, a short distance above its mouth, are in granite, which is more or less decomposed. It seems to have a dip S., SE., and SW. The only place where real granite can be seen is about 30 rods above the mill dam of Mr. Eldridge. It here rises 20 or 30 feet above the creek. In other places the creek runs over it, making rapids and falls, some of which Mr. Eldridge has improved for his mill power.

A substance was met with here for the first time which was afterwards seen at a number of places. Its origin seems to be dependent on the granite. Its association with the granite is so close that it seems to be a result of a change in the granite itself. It lies first under the drift, or under the Cretaceous rocks, where they overlie the granite, and passes by slow changes into the granite. It has somet of the characters of steatite, and some of those of kaolin. In some places it seems to be a true kaolin. It is known by the people as "Castile soap." It cuts like soap, has a blue color when fresh, or kept wet, but a faded and yellowish ash color when weathered, and when long and perfectly weathered, is white and glistening. The boys cut it into the shapes of pipes and various toys. It appears like the pipestone, though less heavy and less hard, and has a very different color. It is said to harden by heating. This substance, which may, at least provisionally, be denominated a kaolin, seems to be the result of the action of water on the underlying granite. Since it prevails in the Cretaceous areas, and is always present, so far as known, whenever the Cretaceous deposits have preserved it from disruption by the glacier period, it may be attributed to the action of the Cretaceous ocean. In some places it is gritty, and in others it may be completely pulverized in the fingers. A great abundance of this material exists in the banks of the Birch Coolie, within a short distance of its mouth.

In the bed of the creek, above the mill-dam, several veins are seen crossing the smoothed surface of the rock. In low water these can be closely inspected, and their composition and structure ascertained. The following sketches illustrate some of their interesting features.

The Structure of Granitic Veins at Birch Coolie.

The vein, a part of which is illustrated by figures below, is in granite, and is made up of granite. The

constituent parts, however, in the vein, are much finer. than in the body of the enclosing rock, and show a deeper tinge of red color. Its direction is S. W., and it is four inches wide. It is visible along the creek 250 feet, and it is crossed by numerous other veins that are mainly quartz itic and narrow. The structure of the main vein is somewhat schistose, and seems to be harder, judging from its forming a ridge that stands above the general surface of the rock one or two inches. The laminae of the schistose vein run usually at some angle across the direction of the vein, but in one place, where there is a slight change in the direction of the vein, they nearly correspond with it. Their usual direction is nearer N. and S. This main vein is faulted in several places, and is divided so as to enclose an irregular oblong area at one point. The fault here sketched is accompanied by a very little quartzitic deposit, but there is no constant vein of quartz crossing the main vein, though there is a small indistinct seam that curves off to the south on the east side. The laminae in the two separated ends of the vein exhibit a curving in opposite directions, as if they had been somewhat elastic or plastic, and by being wrenched apart, had bent toward each other.

Division and Reunion of Vein at Birch Coolie.

The following diagrams represent some of the effects of disturbance in changing the direction and structure of veins. The curvature represented in the first below, is a part of the same vein as described above. It is accompanied by a change in the arrangement of the minerals in the granite, producing a curving, schistose lamination.

Faulting in Vein.

In the second, the same vein is intercepted by a vein that has the outward aspect of orthcclase felsite, which seems to be of earlier date, inasmuch as the former is discontinued on reaching the latter. The discontinuance of the smaller vein seems to have been the cause of a certain ramifying schistose structure in the vicinity of the point of contact of the two veins. The felsite vein is one foot wide, and has a

flesh color, with probably considerable quartz crystallized with it. It also shows some mica. It faults another vein, and hence is of later date than it.

Discontinuance of Vein in Granite at Birch Coolie. Discontinuance.

[For "Compact, Crypto-crystaline blesite," read Compact, crypto-crystalline felsite.]

Granite of the same composition and outward appearance as that below Fort Ridgely outcrops on both sides of the Minnesota, at the mouth of Crow creek, Sec. 35, T. 113, R. 35. It is here also superficially decomposed to the depth of several feet, forming a substance resembling kaolin, already mentioned as occurring at Birch Coolie. The usual points of exposure of this kaolin are in the banks of the little ravines that enter the Minnesota river. It is generally overlain by deposits of Cretaceous age, comprising clay, lignitic shale, sandstone or limestone. When the water carries this kaolin out on to the bottoms, and there spreads it over the surface, it becomes dry after the subsidence of the water, and then appears as a nearly white, exceedingly unctuous, glittering scum covering the ground. In this con