In the United States it occurs from near the sea-level in Arizona, and even below the sea-level in Southern California, up to an elevation of at least six or eight thousand feet, along the eastern border of the Rocky Mountains, and in the elevated valleys of New Mexico, Colorado, and Wyoming. It occupies depressions of all sizes up to valleys having an area of hundreds of square miles. Although occurring throughout the arid region, it can be studied to best advantage in the drainless and lakeless basins in Nevada, Utah, and Arizona. _Composition._—When examined under the microscope, the adobe is seen to be composed of irregular, unassorted flakes and grains, principally quartz, but fragments of other minerals are also present. An exhaustive microscopic study has not been made, but the samples examined from widely-separated localities were very similar. The principal characteristics observed were the extreme angularity of the particles composing the deposit and the undecomposed condition of the various minerals entering into its composition. It is to be inferred from this that the material was not exposed even to a very moderate degree of friction, and had not undergone subaerial decay before being deposited. Adobe collected, at typical localities is so fine in texture that no grit can be felt when it is rubbed between the fingers; in other instances it contains angular rock fragments of appreciable size. The composition of the material is illustrated by the following analyses: ANALYSES OF ADOBE. BY L. G. EAKINS. Constituents. No. 1. No. 2. No. 3. No. 4. Sante Fe, New Fort Wingate, Humboldt, Salt Lake Mexico. New Mexico. Nevada. City, Utah. SiO₂ 66.69 26.67 44.64 19.24 Al₂O₃ 14.16 0.91 13.19 3.26 Fe₂O₃ 4.38 0.64 5.12 1.09 MnO 0.09 trace 0.13 trace CaO 2.49 36.40 13.91 38.94 MgO 1.28 0.51 2.96 2.75 K₂O 1.21 trace 1.71 trace Na₂O 0.67 trace 0.59 trace CO₂ 0.77 25.84 8.55 29.57 P₂O₅ 0.29 0.75 0.94 0.23 SO₃ 0.41 0.82 0.64 0.53 Cl 0.34 0.07 0.14 0.11 H₂O 4.94 2.26 3.84 1.67 Organic matter 2.00 5.10 3.43 2.96 ————— ————— ————— —————— 99.72 99.97 99.84 100.35