STRATIGRAPHY AND PALAEONTOLOGY OF THE FOX HILLS AND 



LOWER MEDICINE BOW FORMATION OF SOUTHERN 



WYOMING AND NORTHWESTERN COLORADO 



INTRODUCTION 



Iii view of the controvcrsial naturc of thc Lancc and rclati>d floras in connection 

 with ]\Iesozoic-Cenozoic boundary problems, it is rathcr disconccrting to find that 

 neither the Lance nor the closely related Medicinc Bow floras have ever been ade- 

 quately studied or described. It is the purpose of this paper to outhne the stratig- 

 raph}' and palseontology of the Medicine Bow formation, and to describe and 

 discuss the fossil plants collected from this formation ckiring the past two years. 

 The study of the Lance floras of Wyoming, Montana, and the Dakotas is in progress 

 and will form the basis of subsequent papers. While my interest is primarily in 

 the succession of Upper Cretaceous floras of the West and their relation to succeed- 

 ing Cenozoic floras, it is hoped that the rcsults of these studies will help to harmonize 

 the conflicting lines of palseontologic and stratigraphic evidence regarding the 

 Mesozoic-Cenozoic boundary in the Rocky Mountain region. 



For many years, confusion has arisen from the practice of including all the coal- 

 bearing formations of the Upper Cretaceous and lower Tertiary in the all-embracing 

 "Laramie Group"; as a result, few of the contained floras could be adopted as 

 standards for comparison in other fields. As in all other branches of stratigraphic 

 palseontology, it is necessary first to establish a standard fauna or flora whose age 

 is definitely known from other lines of evidence. Thereafter, the age of other faunas 

 or floras can be determincd by comparison and contrast. The Medicine Bow flora 

 is admirably suited to serve as such a standard because its age can be rather defi- 

 nitely determined by its relation to both invertebrate and vertebrate faunas of known 

 age. 



The study of the Medicine Bow flora is part of a program on Upper Cretaceous 

 floras of the Rocky Mountain region which I have vmdertaken under the joint 

 auspices of the Carnegie Institution of Washington and Princeton University. The 

 distribution of the 6 localities f rom which the fossil plants were obtained is indicated 

 in figure 1. At each of these locahties the sections were carefully measured by 

 compass-traverses, and the exact stratigraphic position of each plant-bearing 

 horizon was determined with reference to a well-established and diagnostic faunal 

 zone of the underlying Fox Hills formation. Sections were measured by A. P. 

 Conway, Dean Hill, and M. L. Rittenhouse, students at Princeton University, who 

 also identified most of the invertebrates coUected. The invertebrate identifications 

 were checked by Dr. John B. Reeside of the U. S. Geological Survey. Friendly 

 encouragement and constructive criticism have been freely given by Dr. Ralph W. 

 Chaney of the University of Cahfornia. Yaluable suggestions in various phases of 

 the study have been made by Dr. Roland W. Brown of the U. S. Geological Survey, 

 and Dr. S. H. Knight of the University of Wyoming. Herbarium material has been 



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