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Show I l l In the vicinity of Las Vegas a number of channels have been worn into the Creta-oeons strata by tributaries of theGallinas, and thus the succession of strata can be well Btudied. Limestone predominates; then follow slate, sandstone, clay, and lignite. Of rare occurrence, not only here but also in the Cretaceous beds of America generally, is chalk- a mineral whose existence in this country was entirely unknown until Suite recently. The bed of chalk three miles northeast of Las Vegas, in the vicinity of reen's ranch, is 2 feet thick. The material is very soft, of great whiteness, and is used by the Mexicans for whitewashing. It can be used directly for writing, like the English chalk. On treatment with hydrochloric acid but little remains insoluble, and this consists of clay. The solution obtained contaius, besides lime, small quantities of alumina and magnesia. Although in general physical properties and in chemical composition this chalk cannot be distinguished from the English chalk, the miscroscope reveals a great difference. While the latter is largely made up of the microscopic shells of rhyzopods, no trace of organized forms can be discovered in the Las Vegas chalk. It is, therefore, an open' question how this chalk was formed. About a mile east of Green's rauch I noticed a singular phenomenon. The limestone here occurs in rhombic prisms, fitting on each other with regularity and exhibiting a most peculiar- jointed structure, resembling more an artificially paved road than a natural occurrence. I do not myself entertain the belief that this natural regularity is due to a tendency to crystallization, any more than is the formation of six- sided columns of basalt. The primitive blocks have a thickness of balf a foot on an average, and can be used directly for building purposes like bricks. The Las Vegas limestone frequently contains particles of iron pyrites, and in places is very bituminous, exhaling a strong odor of coal- oil, and leaving, on treatment with hydrochloric acid, a black residue consisting of a mixture of carbon particles aud clay. Dolomitic limestone appears to be absent, and while crystalline structure is rather the exception, the rock has generally ft slaty color and grain. It contains from 10 to 30 per cent, of clay, and thus forms hydraulic limestone. Hutf a mile east of Green's ranch is a stratum of excellent cement, as will be seeu from the analysis of a sample: Carbonate of lime 69.98 Carbonate of magnesia. Trace. Clay 28.09 Moisture with trace of bitumen 1.22 99.29 In the best cements the amount of clay is, on au average, 28 to 34 per cent., and I believe there are few localities where this proportion is encountered; hence, this cement may be of great value, at some future time, as an article of exportation. The cement of the commerce of the present is generally an artificial mixture, which,' of course, cannot be as cheap as the natural product. Gypsum and alum occur some ten miles southeast of Las Vegas, but I did not have an op| » ortunity to visit the locality. Although not properly belonging to this chapter, I may here give the analysis of a green feldspar which occurs in some parts of the Rocky Mountains, and especially in the valley of Bear Creek, near Pike's Peak, where it is found in large well- formed crystals. Green feldspar is of very rare occurrence, not more than three or four localities where it exists beiug known. It was a question ot interest to myself to what the green coloration is due. I bad suspected the pr< s nee of copper, but the, investigation showed that the color is due solely to the presence of a small amount of the protoxide of iron. In the following table the result of the analysis is given, ( I,) and for comparison the composition of a green feldspar from Bodeuniais, Bavaria, ( II:) I. II. 8ilicicacid 67.01 63.12 Alumina 19.94 19.78 Protoxide of iron 0.89 1.51 Soda 3.15 2.11 Potassa 8.84 12.57 Lime Trace. 0.66 Magnesia Trace. 0.13 99.83 99.88 The crystals of the green feldspar from Bear Creek are frequently over an inch in thickness, and contain minute cracks and fissures partially filled with hydrated oxide of iron, showing a partial alteration of the mineral. CLIMATOLOGICAL NOTES. During our stay in the extensive mountain region between Abiqnin, Nacimiento, and Jemez, in Northern New Mexico, I made hourly observations of the barometer and |