Geology

Abstract

WITH the exception of a chapter on the general geology of Mongolia by C. P. Berkey and F. K. Morris, this work is devoted to a detailed account of the fauna of the Jisu Honguer limestone of southern Mongolia, with a discussion of its age and relationship to similar faunas of other regions, more particularly to Russia and India. Brachio-pods are the predominating group in the fauna; of these, no less than 99 species and varieties are recognised, belonging principally to the spiriferids, the productids, and the streptorhynchids, with the remarkable form Richthofenia. The Mollusca are relatively few in number, there being only 19 species and varieties of gasteropods and 17 of lamellibranchs. Noteworthy features are the rarity of corals and Polyzoa and the absence of Foraminifera, echinoderms, trilobites, and cephalopods. To account for this limitation of the fauna, combined with signs of dwarfing shown by many of the brachiopods, the author suggests that the salinity of the water was below normal, and compares the conditions with those now existing in Pechili Bay, a nearly enclosed area freshened by the waters of the Yellow River, where some groups of organisms usually abundant in the open sea are rare or wholly wanting.