_Table of Specific Gravities of Sedimentary Rocks of the Henry Mountains._ ──┬─────────────────────────────────┬────────────────┬───────────────── │ Rock. │ Condition. │Specific gravity. ──┼─────────────────────────────────┼────────────────┼───────────────── 1│Masuk Sandstone │Unaltered │ 2.16 2│Blue Gate Sandstone │Unaltered │ 2.14 3│Blue Gate Shale │Unaltered │ 2.45 4│Flaming Gorge Shale │Unaltered │ 2.42 5│Gray Cliff Sandstone │Unaltered │ 2.13 6│Vermilion Cliff Sandstone, (top) │Unaltered (?) │ 2.21 7│Vermilion Cliff Sandstone, (base)│Unaltered (?) │ 2.28 8│Henry’s Fork Conglomerate │Slightly altered│ 2.25 9│Vermilion Cliff Sandstone, │Altered │ 2.48 10│Aubrey Sandstone │Altered │ 2.55 11│Tununk Shale │Altered │ 2.60 ──┴─────────────────────────────────┴────────────────┴───────────────── It is plain from this table that the effect of the metamorphism was to increase the densities of the rocks affected. The Blue Gate shale which _unaltered_ gave 2.45, is lithologically identical with the Tununk shale which _altered_ gave 2.69. The Aubrey sandstone cannot be observed unaltered in the vicinity of the mountains, but at a distance of forty miles where it again comes to the surface it closely resembles the Gray Cliff sandstone. If it has the same normal weight as the latter, then it has increased from 2.13 to 2.55. The specimens of the Vermilion Cliff sandstone numbered 6 and 7 were not visibly changed, but as they were obtained from the flank of the Holmes arch there was reason to suspect that their condition was not normal, and the determined densities strengthen the suspicion. Judged by other localities, the normal density of the Vermilion Cliff rock is not far from that of the Gray Cliff rock, namely 2.13; and it is easy to believe that the upper portion of the bed where it lay on the side of the Holmes arch was changed in density to 2.21; while the lower portion lying nearer the laccolite was changed to 2.28; and while the same bed among the Ellsworth dikes acquired the density of 2.48. Taking into account both these considerations and certain others which need not be enumerated, I derive the following: