290 



THE AGE OF MAMMALS 



tional to the Upper Miocene. Finally the studies of Merriam ' and Sin- 

 clair 2 have confirmed Cope's opinion that the Mascall of Oregon, immedi- 

 ately overlying the Columbia River lava which caps the Upper Oligocene 

 of the John Day Formation, is also of this age. The Virgin Valley of 

 Nevada (p. 350) has recently yielded a fauna of similar age. We are thus 

 enabled to again survey the mammalian life of North America over a wide 

 geographic area extending from the plains to the mountain region, and on 

 the whole very uniform in character. As bearing upon the climate of 



Fig. 143. — Middle Miocene of Colorado. A view of West Pawnee Butte, taken from the 

 summit of East Pawnee Butte. Photograph by American Museum of Natural History expe- 

 dition of 1901. 



these times it is interesting to observe the testimony of the Mascall flora, 

 as described by Knowlton.'* 



Flora of the northwest mountain region. — In the northwest mountain 

 region no palms are recorded (cf. pp. 282-4). The vegetation still bore 

 a southern character. The Mascall flora of the John Day Basin (lat. 45° N.), 

 which is regarded as Middle Miocene, is relatively rich. It was distinctly 

 a hard wood flora, in general appearance like that of the area east of the 

 Mississippi at the present time.^ There were large numbers of horsetails 

 (Equisetum), but the ferns were scarce. Both of the grasses (Graminese) 



1 Merriam, J. C, A Contribution to the Geology of the John Day Basin. Univ. Cal., 

 Bull. Dept. GeoL, Vol. II, 1901. 



- Sinclair, W. J., Some Edentate-like Remains from the Mascall Beds of Oregon. Univ. 

 Cal., Bull. Dept. GeoL, Vol. V., no. 2. 1906, pp. 65-66. 



' Knowlton, F. H., Fossil Flora of the John Day Basin, Oregon. U.S. Geol. Sure., Bull., 

 204, 1902. 



* Ibid., p. 93. 



