Book Description

Excerpt from Obsidian Cliff: Yellowstone National Park A view of the west face of the southern end of the cliff is given in pi. IX. The shining black columns rise from a talus slope which reaches some fifty feet up the cliff. These prisms are fifty or sixty feet high and vary in width from two to four feet near the end of the cliff, the width of each column being quite constant throughout its length. On the south face of this end of the cliff the columns are the same, but grow less clearly defined toward the east, where a sharp bend in the lava sheet has formed gaps in the rock and de stroyed the continuity of the mass; beyond this the columns incline considerably toward the west, as though the underlying surface of contact sloped toward the west also. Farther up the slope to the east they disappear. The columns in the main face of the cliff are tilted 10° to the eastward, and the planes of flow which cross them have an average dip of 10° east, indicating that the underlying sur face at this place slopes toward the east. Along the cliff to the north the columns become gradually broader, the largest being 20 feet in width. The prisms have no uniform number of sides, four, five, and six being those most frequently observed; the sides are unequally devel oped, but at a distance the general effect is quite regular. Toward the north, with the change in the nature of the rock, to be described later on, the broad columns grade into massive blocks formed by vertical cracks much farther apart. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.