3d. The inclination of the arched strata proves that they have been disturbed. If the laccolites were formed in each case before the sediments which cover them, the strata must have been deposited with substantially the dips which they now possess. This is incredible. The steepest declivity of earth-slopes upon the land is 34° from the horizontal, and they have not been found to equal this under water. Prof. J. D. Whitney noted 23° as the original slope of a deposit on the Pacific Coast, and regarded it as an extreme case. The writer has made many measurements of the inclination of oblique lamination in massive sandstones, and found the maximum to be 24°. But the strata which cover the laccolites dip in many places 45° to 60°, and in the revetments of the south base of Mount Hillers they attain 80°. 4th. It occasionally happens that a sheet, which for a certain distance has continued between two strata, breaks through one of them and strikes across the bedding to some new horizon, resuming its course between other strata. Every such sheet is unquestionably _subsequent_ to the bedding. 5th. The strata which overlie as well as those which underlie laccolites and sheets, are metamorphosed in the vicinity of the trachyte, and the greatest alteration is found in the strata which are in direct contact with it. The alteration of superior strata has the same character as the alteration of inferior. This could never be the case if the trap masses were contemporaneous with the sediments; the strata on which they were imposed would be subjected to the heat of the lava, but the superior strata would accumulate after the heat had been dissipated. In the Henry Mountains a large number of observations were made of the phenomena at and near the contacts of sedimentary and igneous rocks, and in every instance some alteration was found. In fine, all the phenomena of the mountains are phenomena of intrusion. There is no evidence whatever of extrusion. It is not indeed inconceivable that during the period in which the subterranean chambers were opened and filled, a portion of the lava found its way to the top of the earth’s crust and there built mountains of eruption; but if such ever existed, they have been obliterated.