6 BULLETIN 169, UNITED STATES NATIONAL MUSEUM 



That this work has been ^vTitten at all is largely due to Dr. Gidley, but 

 he is not responsible for its errors or for any matter in it not expHcitly 

 stated to be his. 



It is further desired to acknowledge how much this work owes to 

 Albert C. Silberling, whose contributions to it go far beyond those 

 usual from a collector. He discovered most of the fossil localities, 

 including all those of real importance, and made far the greatest part 

 of the collection, \vdth skill, persistence, and devotion that cannot be 

 too highly praised. He established a system of field records of the 

 greatest accuracy, used throughout this pubhcation. Even beyond 

 this he so thoroughly examined the field and so carefully studied and 

 correctly interpreted its geology that much of what is here written 

 about it, and of what has appeared in publications by others, is merely 

 reducing to writing observations made by or with him. He is thus in a 

 sense an author and authority of the geologic part of this work, 

 although he has not actually written any of it and is not responsible for 

 misinterpretation of his views or observations. Aside from the long 

 periods when he was definitely employed as a collector, Mr. Silberling 

 has spent every spare moment for the past 35 years worldng in this 

 field, and this memoir is in a real sense the outcome of this lifetime 

 vocation and avocation. 



The following illustrations were drawn by Rudolph Weber under 

 Dr. Gidley's direction: Figures 22, 30-34, 37-41, 446 and b', 59, 63a, 

 71a and a', 72, 736, 80.^ The other dramngs were made by Sydney 

 Prentice, under my direction. The accompanying map is based on 

 field work by Silberling and me and was drawn by John C. Germann. 

 The field photographs were taken by me. 



The late Prof. W. J. Sinclair, of Princeton University, lent and per- 

 mitted the description of the specimens collected for that institution 

 by Douglass and by parties under Farr. Dr. G. L. Jepsen has facili- 

 tated comparisons with specimens collected under his leadership for 

 Princeton in the Fort Union of Wyoming. The Carnegie Museum, 

 through J. J. Burke, lent material in their collection from this field. 

 I am much indebted to these institutions and colleagues, as well as to 

 officials of the United States National Museum, particularly Dr. Wet- 

 more and Mr. Gilmore, for their support of the work and constant aid 

 and encouragement, and of the American Museum of Natural History 

 for the time and facilities provided. 



PREVIOUS WORK 



Discovery of Paleocene* mammals lagged behind that of typical 

 faunas of any later epoch, or even of the Mesozoic. This slowness of 

 discovery and the factors of scarcity of fossils and difficulties of study 



' In a few cases Prentice has modified these drawings slightly. 



* "Paleocene" is granted to be an epoch of the Tertiary, including post-Lance or post-Danian and pre- 

 Qray Bull or pre-Sparnacian time. 



