Excerpt from Stratigraphic Notes, 1983 Twist Gulch Member and a lower Twelvemile Canyon Member. Industry and university geologists use the name as a direct replacement for the term Twelvemile Canyon Member. This dual usage has caused much confusion. In an attempt to resolve this problem, we propose that the Twist Gulch Member be raised to formational rank, that the units now grouped as the Twelvemile Canyon Member be known as the Arapien Shale, and that the name Twelvemile Canyon Member be abandoned. Although this proposal infringes aspects of both the old and new codes of stratigraphic nomenclature, we believe that widespread and common usage argues persuasively for this change. 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.