8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 128 



planation, appeal is made to the highly disconformable relationship 

 between Eocene and Oligocene strata. An immature-jaw fragment 

 collected by Van Houten from beds undoubtedly a part of the Beaver 

 Divide conglomerate resembles Protoreodon, but the two lower teeth 

 preserved are not truly diagnostic so that a small species of Agrio- 

 choerus may well be represented. It would seem, from a review of 

 the Beaver Divide materials and occurrences, and from field informa- 

 tion furnished me by Van Houten and others, that the Duchesnean 

 interval is not represented by sediments in the Beaver Divide. The 

 hiatus in time is further indicated by the marked disconf ormity. 



A portion of the Sespe formation as exposed to the north of Simi 

 Valley in southern California has been demonstrated by Stock to 

 include strata of at least two horizons of upper Eocene age. The 

 lower of these, as represented by locality i8o, also known as Tapo 

 Ranch, produced Leptoreodon {H esperomeryx) edzuardsi and is about 

 equivalent to Uinta C. Significantly higher and possibly equal to 

 Lapoint in age, locality 150 produced the remains of Simimeryx 

 hudsoni. No Artiodactyla are known from the earlier Poway con- 

 glomerate in San Diego County. 



The Eocene on Sage Creek in western Montana, I am informed by 

 H. E. Wood 11,^ is surely Uintan. The collections from here, now in 

 the Carnegie Museum, contain protoreodont remains, 



ENVIRONMENT 



Certain rather general conclusions seem evident regarding the en- 

 vironment that existed during upper Eocene time in the portion of 

 the Rocky Mountain region in which much of our upper Eocene fossil 

 material has been obtained. Perhaps the most significant information 

 forthcoming is derived from the changing lithology observed in the 

 upper Eocene sequence of the Uinta Basin. This pertains to the 

 transition from the lake deposits of the Green River formation, as 

 represented in Utah, to the predominantly greenish-gray sediments 

 of the Uinta formation. The transition is not abrupt, but there is an 

 interfingering between the fluviatile or flood plain sediments with the 

 deltaic and lacustrine sediments, denoting a periodic retreat of the lake 

 and an overall reduction and eventual disappearance. Furthermore, 

 the upper part of the Uinta formation intergrades laterally and is 

 superseded by a red f acies, the Duchesne River formation, which owes 

 its origin to a transgression of sediments from a different source.* 



2 Oral communication. 



* I am much indebted to Dr. John Qark for an understanding of upper Eocene 

 sedimentation in the Uinta basin. 



