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Show RECONNAISSANCE IN THE UTB COUNTRY. 73 Uo. Name. Locality. 34. Senator West Mountains. 35. Union Gap Las Animas District. 36. Mountain Boy Baker's Park. 37. Scotland Lake District. Geological observations from the mouth of Lake Mary Canon, via Lake Fork of the Grand River, to Del Norte. At the south end of Lake Mary Canon is a heavy formation of soft gray and blue shale, in horizontal strata. The west wall of the canon is of red porphyry, which is mostly covered with coarse conglomerate, often in walls 800 feet in height. The east wall constitutes the west flank of Bristol Head, and is wholly of igneous origin. High up on this wall, coinciding nearly with upper timber- line, are remnants of white and colored clays, formations of which once nearly tilled this canon, and this, too, previous to the conglomerates, as at several localities I found the former combined with the latter. The trail to the Clear Creek Falls was mostly over porphyry and trachytes; thence the valley of Clear Creek was undulating, with but few outcrops, to near the close of the march. Immediately east of Camp 43 is a high ridge of loose, disintegrating brown trachyte, of the character observed on yesterday lower down in the valley. But few outcrops to the summit of the pass to the Lake Fork, elevated ( ascertained by one observation) 11,356 feet.* The summit and the heads of valleys on the north comprise a beautiful undulating surface, as far as the eye can reach,^ embracing thousands of acres of rich soil, indicating an active growth of vegetation in some seasons of the year. On descending into the valley of the Lake Fork of the Grand Biver, white and yellow clays were encountered, similar to those of Lake Mary Canon. The bright colors of these clays are visible far down the valley, often coinciding with timber- line. The older formations are of slate and quartzose porphyry. The wall- rock of the San Cristobal Falls is of trachyte, which had partially filled a portion of the valley, and is disintegrating at some localities, and resembles that observed near Camp 43. At an elevation of about 500 feet above the falls, on the right side of the stream, is what is claimed as a vein of galena rich in silver. It had been but partially opened, and the claimants not being present, little or no information could be obtained. I could discover no indications of a regular or true lode. Quartzose and porphyry seemed to be the prevailing formations on the lower side, and, a short distance above, slate. I gathered a few specimens of the ore, which are represented by No. 37 in the collection. A solitary cotton- wood at Camp 45 is the only specimen found by me at so great an altitude. Below Camp 45 are few outcrops, principally red trachyte porphyry. The mountain- sides are stained with red and white clays to near upper timber- line. There were but few outcrops for seven miles below Camp 46, excepting a few fragments of conglomerates. At the eud of this distance we passed through Great Gate, a narrow gorge of about three furlongs in length, with walls of trap. Thence down to Lake Fork Canon, the lower slope of the valley is mostly of red trachyte porphyry. Near Camp 47 is a dike of feldspathic trap. The high ground flanking the canon on the west is composed of feld- * Thi8 elevation may be considerably wrong, as the United States Signal- Service reported a terrific storm to have occurred to northwest and west of the Mississippi River on the night of this day. |