A GLASS MOUNTAIN.

New Zealand Herald, Volume XXIII, Issue 7824, 18 December 1886, Page 2 (Supplement)

A GLASS MOUNTAIN.

Ons of the forthcoming reports of the United States Geological Survey will contiin a paper by Professor Joseph P. Iddings upon an obai dian cliff in Yellowstone Park. This cliff is an elevation half a mile long by from 150 ft to 200 ft high, the material of which, Professor Iddings says, " is as good a glass as aay artificially manufactured." Its colours and structure not only make it highly interesting to the visitor, but furnish to the scientific investigator phenomena of importance. The chtf presents pare of a section of a surface flow of obsidian which poured down an anciei.t slope from the plateau lying east. It is impossible to determine what the original thickness of this flow was. The dense gl&ss which now forms its lower portion is from 75ft to 100 ft thick, while the porous and pumiceous upper portion has suffered from ages of erosian and glacial action. A remarkable feature of the cliff is the development of prismatic columns, which form its southern extremity. These are of shining black obsidian, rising from the talus slope, and are from 50ft; to 60ft in height, with diameters varying from 2ft to 4ft- The colour of the material of this cliff is for the most part jet black; but much of it is mottled and streaked with bright brownish red and various shades of brown, from dark to light-yellowish, purplish, and olive green. The brilliant lustre of the rock and the strong contrasts of colour with the black are very striking. In places the glass in the process of cooling has been broken into small angular pieces, which have been again cemented by the later flow, producing many coloured and beautiful breccia. In some places the material shows a fine satin lustre ; while in others a deep golden sheen is noticeable, which, under the lens, resolves itself into thin beams of red and yellow light Through the black and red glass are scattered dull bluish grey patches ana bands and round grey and pink masses, the effect of which is to still further vary the appearance and beauty of the rock, and make it the moet conepicuoue and characteristic variety of volcanic lava known.