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THE UNIVERSITY OF ILLINOIS LIBRARY From the collection of \ Julius Doerner, Chicago Purchased, 1918, cl. 5 57,3 v.? Digitized by the Internet Archive in 2015 https://archive.org/details/annualreportofpr7187tran DEPARTMENT OF THE INTERIOR. REPO II T OF THE UNITED STATES GEOLOGICAL SURVEY OK THE TERRITORIES. F. V. IIAYDEN, UNITED STATES GEOLOGIST-IN-CIIARGE. VOEUME VII. WASHINGTON: GOVERNMENT PRINTING OFFICE. 1878. I LETTER TO THE SECRETARY. Office of the United States Geological and Geographical Survey of the Territories, Washington, D. C, January 1, 1878. Sir : I have the honor to transmit herewith, for your approval and for publication, the Seventh Volume of the Final Reports of the Survey under my charge. The work consists of a Report on the Tertiary Flora of the West, *by Prof. Leo Lesquereux, of Columbus, Ohio, being Part II of ''Contributions to the Fossil Flora, of the Western Territories" — Part I being "The Cre- taceous Flora", by the same distinguished author, whose long-continued studies in palaeo-botany have placed the subject upon a firm and enduring basis. Part I formed Vol. VI of this series of Final Reports, and the present Part constitutes Vol. VII. The circumstances which led to the preparation of this work may be briefly reviewed. When the geological investigation of the Lignitic formations of the West had reached a certain point, the conclusions derived from such studies were discussed by certain geologists who dissented from the views then expressed respecting the age of these strata. It consequently became desirable, in order to the solution of the questions involved, to elaborate further, and with the greatest care, all available material bearing upon this interesting problem. To this end, I desired Prof. Joseph Leidy, Prof. E. D. Cope, Mr. F. 13. Meek, and Prof. Leo Lesquereux, to present in detail all the evidence they could secure in their respective specialties of Extinct Vcrtebrata, Extinct Invcrtebrata, and Fossil Flora, bearing on the disputed age of these formations, to decide, if possible, whether the strata in question are Cretaceous or Tertiary. The various reports which these gentlemen have furnished testify with what zeal, ability, and success these instructions have been carried out. ui IV LETTER TO THE SECRETARY. If objection is made to the use of the term "Lignitic'' Group, I would say that, in this work, it is restricted to a series of coal-bearing strata lying above the Fox Hills Group, or Upper Cretaceous, and these are embraced in the divisions Laramie and Fort Union Groups. It is well known that there are in various parts of the West, especially along the fortieth parallel and south westward, very thick beds of coal in the various divisions of the Cretaceous, extending down even into the Upper Jurassic. Had this not been the case, the more general term Lignitic would have been retained by this Survey, in preference to any other. As far back as 1859 it was' my belief, founded on what appeared to be sufficient evidence, that the sequence between the well-characterized Creta- ceous strata and those of the Lignitic Group, as defined at that time, was continuous, and that the chasm which was supposed to exist between the Cretaceous and the Tertiary epoch would be found to be bridged over. This belief was not based on strictly pakeontological evidence, for no well-marked Cretaceous fossils were then known to pass up into the Lignitic or brackish beds. But the physical conditions under which the sediments of the upper strata of the Fox Hills Group were deposited indicated a gradual change, -from deep, quiet marine seas to shallow waters, which became at length brackish and finally entirely fresh waters, during which time the purely marine invertebrate fauna perished, a brackish and purely fresh-water fauna taking its place. This condition of the Lignitic Group covered a vast area in the Northwest, extending far southward, along the eastern slope of the Rocky Mountains, to Denver, Colorado. As we proceed southward and westward from the Missouri River, the brackish beds increase in thickness until along the fortieth parallel they become three thousand feet or more, indicating, so far as can be determined, no break in the sequence from the Fox Hills Group to the purely fresh-water strata of the Wahsatch Group. Dr. C. A. White, Paleontologist to the Survey under my charge, has made a critical examination of these formations during the past season, and lie says that his investigations have fully confirmed the views expressed by me some years ago, and indicated by the palasontological studies of Mr. Meek, that the Fort Union beds of the Upper Missouri River are the equivalent of the Lignitic formation as it exists along the base of the Rocky Mountains in Colorado. He also testifies to the equivalency of the latter with the Bitter Creek series west of the Rocky Mountains. These views of Dr. White are con-