The Characteristics of Various Types of Conglomerates

Abstract

In the prosecution of a recent study of the Roxbury Conglomerate (Boston, Mass.), the writer found himself in need of criteria by which to determine the mode of origin of that formation. A critical examination was therefore made of the published descriptions of conglomerates in many parts of the world and belonging to many geological ages, in the hope of discovering characteristics sufficiently marked to distinguish one type from another. The data collected and the conclusions derived therefrom have recently been published in detail.2 The present paper is a brief summary of the results of the investigation. Five general types of conglomerate were considered, namely: marine, fluviatile, estuarine, lacustrine, and glacial. In addition to these, another type was studied, commonly known as crush-conglomerate, but really pseudo-conglomeratic in its nature. The fact was recognized that many conglomerates are the product of the combined action of several conglomerate-forming processes, but the results of each process were classified separately. Among the formations taken under consideration were: the Cretaceous formation of Texas, as described by Hill;3 the Pottsville Conglomerate; non-marine formations in India, Persia, Great Britain, and the United States; the Devonian of Pennsylvania and Maryland, as described by Willis;4 the Newark formation as described by Russell;5 glacial deposits of the Quaternary period in the United States and Europe; ancient glacial deposits in India, Australia, South Africa, and Norway; and crush-conglomerates in the Isle of Man and Argyllshire. ' Read before the Geological Society of America, December 28, 1906, New York. 2 Museum of Comparative Zoology, Bulletin No. XLIX, Geological Series, 8, 1906. 3 R. T. Hill, U S. Geological Survey, Twenty-first Annual Report, 1901, pt. 7. 4 Maryland Geological Survey, 1902, Vol. IV, pp. 21-935 U. S. Geological Survey, Bulletin No. 85, 1892.