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Show 99 horn Creeks, on the eastern slopes of the Sierra Mojada, the limestone beds are exceedingly rich in cretaceous shells. Calcite occurs also in very large crystals. From the head of Greenhorn Creek to that of the Red Creek, a bed of conglomerate of great thickness extends, which, uear the head of the latter, consists of granules of feldspar and quartz, with here and there particles of muscovite. The cementing substance ia a reddish clay, and the quartz- pebbles present a rounded appearance as though worn considerably. The beds of this conglomerate dip 520° to 22°. 8 « » nie ten miles west of Red Creek, the Hardscrabble Creek, another tributary of the Arkansas, leaves the mountains. There may be seen quite a number of interesting phenomena due to glacial action ; morainal deposits, polished quartz, rocks, and scattered bowlders testify to former glacial phenomena of grandeur and magnitude. The canon of Hardscrabble Creek is formed on both sides by sandstone strata, which dip 60° to 70°. The declivities thus formed are perfectly barren, although the valley immediately beneath is covered with a vigorous forest vegetation. The barrenness of these declivities, however, is not due to climatic influences, but solely to their great inclination, whereby the soil is prevented from taking hold. Crossing the crest of this noithern portion of the Greenhorn Mountains we descend to the recent mining town of Rosita. As regards the silver- mines of this section, the reader is referred to vol. I of the quarto series of reports. We only allude to them here as regards their geological position. The Victoria and Seuator lodes are true fissnre- veins of galeniferous quartzite in the traehytic porphyry, while the others, northwest of these, are chiefly situated in sedimentary rocks. Clay strata containing particles of chloride of silver form qnite extensive beds. These sedimentary deposits have a considerable dip- 30° to 45°- a result produced by the disturbances which accompanied the later volcanic eruptions in the vicinity. Slides are also noticed in several instances; one of 25 feet occurs on the Victoria lode. A mile southwest of Rosita, on the southern slope of a hill covered with quartzitio debris, are masses of round siliceous concretions, from the size of a nut to that of a human head, scattered about profusely. These the miners call " petrified heads," defining the contortions here and there upon the globes as the brain turned into stone. At a glance we may recognize in them the results of siliceous waters formerly existing here, results analagous to tho deposits and incrustations observed with the siliceous geysers of Montana and Idaho. No clue as to the exteut and position of these hot springs can at present be found in Wet Mountain Valley, time having covered up their former sites by the rubbish of the ages. Passing a little farther south, over a low, hilly country, with mighty mountain chains on either side, we reach the head of the Muddy, a tributary of the Huerfano River. While sandstone predominates at this point, a few miles to the westward, between tho neighboring foot- bills of the Sangre de Cristo Mountains, we meet with syenite and amphibolite, and on the Cuerno verde Peak, to the southwest, with syenitic granite. This peak is an interesting structure. Its lower portions are covered with sandstone, then follows granite, the top being formed by volcanic masses. Fifteen miles to the south of the head of the Muddy we cross the Huer-fauo River. While here the chief rorks are sandstone and conglomerate, the neighboring hills are covered with dibrin and pebbles of granite, trachyte, and basalt-drifts from the mountains. About four miles west of Gardner's Store, a little settlement in the Huerfano Valley, are some very steep and barren peaks, the so-called Sheep Mountains. These have an elevation of 8,400 feet, and consist of a purplish rhyolite, exceedingly rich in silica, with large sanidin crystals sparingly embedded. The mountain- Hides are covered with small sharp fragments of rock, evidently yielding, but very difficult to disintegrate. About half a mile south of Gardner's Store a steep trachyte butte, of about 1* 50 feet in height, stands sentinel- like in the valley, and forms. an abinpt contrast with the surrounding undulating surface. This trachyte is of a fine- grained gray matrix, in which numerous hornblende crystals are embedded. In most of the creeks of the Huerfano Valley gold has been discovered, but in very little quantity. The agricultural lands of the valley are valued at $ 17 an acre, on the ground that they are mineral lands. If the small quantity of gold referred to did not exist in this valley, these lands would, like, the other agricultural lauds hereabout, be valued at only $> l. f> 0 an acre. Formerly, some fifteen miles southwest of the Huerfano Park, in the vicinity of Placer Creek and east of Baldy Peak, a conspicuous, bairen peak of the Sierra Blanca, good placers existed. These placers, called " Gray Back," have, according to a statement made to me, been worked with considerable success fifty years ago by Mexicans, and for a tane by Kit Carson. At these placers we met three poor- looking individuals, who complained of the meager results of their labors; they had hardly cleared * Jf> cents a day from their gold- search. They considered the placers worked out and exhausted, and intended leaving at an early day. The gold is found iu reddish clayey and siliceous deposits, rusty quartzites, and conglomerate, forming beds along the Placer Creek, which are bordered by gueissic and granitic hills. To the east and northeast of these hills paleozoic limestone occurs iu great masses, with Btrata much tilted and displaced. The main rocks of the neighboring Cerro Blanco, the highest aud most southern portion of the Sangre de Cristo Mountains, are |