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Show 102. From zeolites, the carbonate of lime met with in basalts may often be derived. Chemistry forbids the assertion that carbonate of lime is an original constituent of certain basalts; still, the occurrence of carbonate of lime in the amygdaloid spaces of basalts is quite frequent in New Mexico. As we leave the base of the mountains and ascend, basalt disappears, trachyte taking its place, with rhyolite, pumice, and obsidian as accompaniments. The pumice covers a great area some six miles west of Ildefonso, while the obsidian is met farther up, forming large, massive rocks, and assuming quite a porphyritic appearance by its inclosed radiating masses of zeolite, ( spherulite.) Especially is this the case in the northern portions of the Valle Grande, a great mountain park near the Jemez Peak. The creek that runs through that portion was called by our party Obsidian Creek; it forms one of the head branches of the Jemez Creek. In some cases the obsidian is nearly colorless; geuerally, however, it is of the usual black, glassy appearance. Pebbles of obsidian are a conspicuous feature in some of the conglomerates aud tufas in the vicinity of Cerro Pedernal, where the Rio Polvadera and Ojo de Cuerpospin unite to form the Rio de Canoues, a tributary of the Cliama. In this vicinity, as well as farther south in the valley of the Obsidian Creek, are evidences of the glacial epoch, prominent moraines extending far down into the valleys adjoining the peaks. It is a remarkable feature of this plateau that almost every spring here has a higher temperature than is usually the case in such altitudes. Several large springs, full of trout, in the valley of Obsidian Creek have a temperature of 56° F., and this appears to be the temperature throughout the year. It was the same in June, 187U, when we passed these springs, as in September, 1874 ; and in the morning, with the air- temperature below the freezing- point, it was exactly the same as in the afternoon, when the thermometer showed G<)°, which is evidence that the supply of water from beneath is so rapid that external changes of temperature do not apparently affect the temperature of the spriugs. Several miles west of this place, where the Obsidian Creek enters the canon- the head of Caiion de San Diego- are four springs with a temperature of 84° F., the warm waters of which concentrate near by, formiug a sort of swamp, in which many of the lower order of animals have an existence otherwise impossible in this cold region. Here a large nenropterous insect with red wings deposits its eggs, the larvw growing up in the warm pool. Frogs, nowhere else to be seen in these nioutaius, abound here in great numbers. A plant, Ceratophyllum dtmcrsum, grows vigorously iu this swamp. Leaving this poiut and proceeding four miles down the caiion, our attention is arrested by a column of steam rising from among the pine trees on the bluffs. Ascending ab » ut 160 feet from the eastern margin of the stream, we meet with a large hot. spring, called by our guide Spring San Antonio, the temperature of which is 10.">° F. The water is tasteless. The only mineral constituent it appears to contain is carbonate of lime, which forms thin crusts over the rocks with which the water conies in contact. Where the stream of hot water reaches the creek its temperature is 88°, while that of the water of the creek proper was 50°. ( September 10. Air- teinperature, 50° F.) After the mingling of the waters the temperature was 59° F. From these data it follows that the volume of the stream of hot water is 9.7 per cent, of that of the creek. A few miles below this locality the second head branch of the Jemez Creek comes in. This branch has numerous side canons, among them one of great interest from its having a forest of columns resembling in figure but excelling in grandeur those of the Garden of the Gods, near Manitou, Colo. This locality we mimed Monument Cafion. These columns vary in thickness from 1 to 8 feet and iu height from 10 to 50 feet, and are crowned with a large head ot solid rock. The material of those columns is a conglomerate of trachytic pebbles and sand, washed from the adjacent declivities, whence came the blocks also which form the heads of the columns. The explanation of the formation of these columns is simple. Formerly the entire cafion was tilled with sand, debris, and bowlders. The mass of sand beneath a large bowlder was, of course, subjected to a higher pressure than the neighboring strata, aud hence the particles were better cemented than was the rest, and when afterward the erosive power* commenced their work, the softer parts succumbed while the cylindrical masses, with their bowlders as heads, resisted and remained. Proceeding some fifteen miles farther south, in Caiion de San Diego, we reach the interesting Jemez hot spriugs, described in Vol. I l l of the Survey Reports. Near these springs the Carboniferous strata are well exposed, and Spir{ fer earner at us, Prodactus striates, and P. 8eniireticulatu8 are found in abundance. The red sandstoue overlying the Carboniferous limestone contains here and there small deposits of copper- ore, chal-cocite and malachite, with impressions of Calamites. Two miles south of the Jemez hot spriugs are the ruins of a smelting- furnace, but the scanty supply of copper- ore in the sandstone of course did not justify miniug and metallurgical operations. From this point down to the junction of the two great canons ( Canons de Sau Diego and Guadalupe, both from 800 to 1,400 feet deep,) are exposed in the sandstone side-walls a great number of trachytic dikes, all in a vertical position, while iu a number of places the sedimentary strata are much displaced aud inclined. |
