The map is from a tracing of a manuscript copy of Brooks' Map, 1 inch = 200 feet, in the possession of the Republic Iron Co. The area represented on the large scale covers a little more than the N. W. 4 of the N. E. 4 of Sec. 18, T. 46 N., R. 29 W. The sketch to small scale shows the relation to the trough as a whole. (Fig. V.)

Below the magnetite-actinolite-schists and separated from the nearest exposure by a covered interval of 50 feet is the outcrop of quartzite discovered by Pumpelly and Credner. The outcrop runs about 175 feet along the strike and 30 feet across it. At the N. E. end the strike is about N. 55 °E., and at the S. W. end about N. 20° E., the dip in both cases being to the W. of N.,40°-45°. For the most part the rock is massive and heavily bedded, but the higher portion shows unmistakable sedimentary banding, and even false bedding.

In external appearance and in composition the rock is a very coarse-textured, light-colored quartzite, made up almost entirely of quartz, with some muscovite and chlorite as subordinate constituents. Under the microscope, probably because obliterated by shearing, no original rolled grains were seen, although several slides were examined. Red garnets are occasionally found

in the quartzite.

A short distance south and west of the quartzite is a ridge running a little east of north, made up mainly of granite, which presents several bold faces to the west. Near the south end and on the west side, is found upon the granite a westerly dipping fringe of conglomerate, which extends some 50 feet along the strike, as a continuous rock mass. Farther north occasional small patches of conglomerate on the northwesterly sloping granite faces, indicate that the contact follows very closely the direction of the ridge, and lies near its western base.

III. GRANIte.

The granite exposed on this ridge occurs in both white and reddish weathering varieties, which appear to be, however, identical in composition and age. The rock is a coarse mixture of quartz and feldspar of which orthoclase is an important part, and which occurs in Carlsbad twins up to two inches in length. Light colored mica and biotite are largely developed in the planes of shearing. The granite contains much pegmatite, both in veins and in irregular masses. From the contact with the conglomerate back as far as exposures extend, the granite is

traversed by a rude cleavage, which has a general northwesterly direction, and so makes a large angle with the line of contact. The direction of cleavage varies between the limits of N. 40° W. and N. 60° W., and is usually represented by a multitude of planes, in which the micas only are foliated. This cleavage is more strongly developed on the western side of the exposure, near the contact, than elsewhere; and as the cleavage becomes more perfect, the large orthoclase crystals disappear.

IV. CONGLOMERATE.

The matrix of the conglomerate varies between a somewhat micaceous quartzite and a fine grained mica-schist, and shows very distinct bands differing in color, texture, and composition. These bands are thrown into little folds, about northwesterly plunging axes; in strike they conform to the direction of the line of division between the conglomerate and the granite. In this quartzitic matrix are imbedded clearly water-rounded pebbles of quartz, granite, and of a black crystalline schist. The quartz pebbles are as a rule small, few exceeding six inches in diameter. They are of different varieties, clear, milky, brown, and blue gray quartz all being represented. All are more or less thoroughly granulated. They are of very different shapes, and within the planes of bedding, their longer axes lie in different directions. All agree in being smoothly worn and are unmistakably water-rounded.

The granite fragments vary in size from pebbles a fraction of an inch up to bowlders five feet in diameter. The larger are usually thin slabs lying with their flat sides parallel to the bedding. The foliation of the matrix often follows round the inclusions. The contacts between pebbles and matrix are exceedingly sharp; sometimes, however, where several pebbles lie close together, it is a matter of some difficulty to trace the boundary of each on the weathered surface. The distribution of pebbles is very irregular. Near the south end of the exposure they are closely packed, while the northern part of the main exposure has comparatively few. The granite of the pebbles and bowl

ders appears to be identically the same granite as that on which the conglomerate rests. We find both the white and the redweathering varieties represented among the pebbles of the conglomerate, and perhaps also the coarse pegmatite. Figures I and II from a sketch made to scale in the field show the appearance of the rock on the dip surface, while Fig. III, drawn to the same scale, shows the outlines of two medium-sized granite bowlders, as seen in cross section on a joint plane.

V. CONTACT.

At the south end of the main exposure, a nearly vertical cross joint plane on the south of which the rocks have been removed, shows the contact for eight or ten feet across the strike. The relations are represented in Fig. IV.

The conglomerate can be followed by its pebbles with great certainty. The granite below is equally unmistakable. Between the lowest pebble layer of the conglomerate and the undoubted granite, is a zone a few inches wide, that is difficult to assign with certainty to either rock. The contact otherwise is very definite and follows the dip of the conglomerate pebbles. There is no indication that the contact is not simply one of erosion. As the matrix of the conglomerate has been transformed into a crystalline schist as the result of shearing, one may easily suppose that the doubtful zone represents either recomposed granitic detritus or the broken up material of both rocks due to movement along the contact during the folding.

At the north end of the main exposure we have another natural section on a cross vertical plane, shown in Fig. VI. Here a large semi-detached mass of granite, which seems to be joined at the east end to the main mass, lies over a portion of the conglomerate. At its west end it includes a folded fragment of the conglomerate matrix four or five feet long, and two or three feet across, shown at B in the figure.

The junction between the quartz-schist and the granite is sharp, and the banding of the schist is cut at a small angle by the granite. At the east end of the granite mass, at A, a ver