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Show 107 prehension, if we consider that the liquid interior of the earth is most probably composed of concentric layers of different materials placed in the order of their specific gravities. Beneath the granite we find the molten trachytes, and beneath these the basalts, the latter forming the ferruginous slags of the iron center of the earth. The existence of the latter can be inferred not only from the calculated specific gravity for the interior of the earth, ( 8,) bnt also from the earth's magnetism. This iron is, in all probability, identical with the meteoric iron; i. « ., it contains nickel and cobalt, judging from the# presence of these elements in basalts, which I have demonstrated in a former report.* ( Vol. III. Survey Reports.) Taking the trail from San Mateo, a Mexican village on the northern foot of Mount Taylor, to Laguna, situated southeast of this mountain, we find ourselves, on emerging from the forest, upon a high, perpendicular bluff, where a grand panorama meets the view. Before us is a wide, level country, bordered in the east by the Sierra Zandia, and in the south by the Ladrone, Madalena range, and Sierra Mimbres. The sheet of basalt on which we stand is fully 30 feet thick, and rests upon a sandstone stratum exposed to a height of 700 feet. Leaving Chaporero. a small Mexican settlement on the base of thisblnff, we descend, a short way off, another bluff, or wall, of sandstone, 300 feet in height, and reach Povate, an Indian town. A few miles south we pass another terrace, 200 feet in height, and soon afterward one at Laguna. Sixteen miles south of west from this Pueblo is another Indian village, Acoma, on a sandstone mesa 200 feet high. No basalt is seen in this vicinity, bnt it covers large areas to the north and northwest. The country between Laguna and Acoma is a barren, sandy waste, npon which huge masses of sandstone and mesas rest, and which is partially covered by juniper woods. The sedimentary strata at Laguna are all of Cretaceous age. The lower strata consist of red sandstones and marls, the upper of yellow calcareous sandstones with seams of shale. Taking from Sheep Spring, five miles east of Laguna, a straight northeasterly course we reach 8an Ignacio, on the banks of the Rio Puerco, after a journey of thirty miles. This stretch is covered the entire way by the deposits of the Cretaceous period, sandstone being the predominating mass, followed by marls and clays, then gypsum aud brown coal. Pebbles of flint and jasper occur in great numbers, but fossils are unusually rare. Here and there are' ammonites or an Lnowramus. Here ie the southern continuation of the great mesa system of the Nacimiento desert. Some eight mile* above the town of San Ignacio the Rio Puerco emerges from a cafion, but near this town the valley is very broad and evidently is the result solely of erosion. The Cretaceous formation does not cease here, but extends without interruption eastward to the Rio Grande and Jemez Creek. The mesas, however, disappear gradually, their places being taken by an undulating country covered thickly with loose, heavy sand. At Santa Ana, an Indian town on the Jemez Creek, we again encounter the basalt, which here also covers immense tracts of land on both sides of the Rio Qrande. It extends westward from Santa Ana, northward as far as Jemez and on the east side of the Rio Grande from La Bajada to San lldefonso. This immense sheet of basalt is bordered on the east side by the Cerillos, a chain of hills principally of volcanic origin, where we again find basalt and trachyte associated. These hills are some seventeen miles southwest of Santa Fe\ and not only has silver been discovered in them in several places, but also a rare gem- turquoise. On, e of these hills, not far from the bed of the Galis-teo, and consisting of a light purplish trachyte with small crystals of sanidine and" hornblende, is traversed by numerous seams of green and blue turquoise from | to J of aii inch thick. The fine sky, bine color, however, is rarely found with these turquoises, and all the larger seams exhibit a dirty green coloration. How this gem was deposited in the fissures of the trachyte is a mystery. It certainly was not an original constituent of this rock, as may* be inferred from its containing water of hydration. In the few other localities where tnrquoise was found it occ urs in clay- slate or quartzoze schist, and forms also narrow seams. The finest turquoise is found in Persia in the neighborhood of Nichabaur; other localities where it occurs are in Arabia, Asia Minor, and Silesia. As thus far turquoise had been but rarely investigated, I deemed it of interest to determine the composition of that of the Los Cerillos. The fact was thus revealed that it contained over 12 per cent, of silicic acid, a substance not found before in this gem, and as I was very careful in the separation of the seams of turquoise from the trachyte, this cannot be attributed to an admixture of trachyte particles. In the following table is given the analytical result ( I); also ( under II) the composition of Persian turquoise, as ascertained by Church : |