Excerpt from Bulletin of the Southern California Academy of Sciences: Vols; 52-54; 1953-1955 There is an unconformity at the top of Member I which cuts out the upper part to the north and northwest so that in the Grand Canyon area the distinctive unit is not recognized. Member II. This rock unit differs lithologically from the others by its high content of chert. In the Black Mesa region north of Chino Valley it is light-gray, slightly-pinkish, fine-grained, po rous, cherty limestone. The white to light-gray fossiliferous chert occurs in nodules which develop into layers of large, flat, nodular chert in the upper part of the member. The porosity in the lime stone matrix is the result oi differential solution of tiny crinoid stems. Southeastward the limestone has not been affected by solu tion so it is grayish-white, crystalline, crinoidal, and continues to have the cherty layers. Overlying beds lack the chert, so that the contact between Members II and III is rather sharp. Although fossils are not common in this member, a few corals have been collected and are described. The thickness of the member varies from 50 to 100 feet. 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.