FOX HILLS AND LOWER MEDICINE BOW 35 



sary in this region bcfore the details of stratigraphic position, associated vertebrates, 

 invertebratcs, and plants can be uscd to determine the true sequence and age 

 relationships. 



Vermejo-Raton floras — The Vermejo and Raton floras were described by 

 Knowlton ^ as two distinct floras occurring in beds which were separated by a 

 definite unconformity. Although I have not visitcd this region, it secms apparent 

 from the pubUshed descriptions of sections that the evidence for the unconformity 

 can in most cases be interpreted as due to local stream-channeling. Table 4 shows 

 that there are 12 and 11 Medicine Bow species in common with the Vermejo and 

 Raton floras, respectively. In my opinion, this indicates that the unconformity, 

 if it does exist, represents very little if any hiatus. If the Vermejo-Raton floras are 

 combined they possess 20 species in common with the flora of the lower Medicine 

 Bow formation, suggesting that at least a portion of the Vermejo-Raton sequence 

 is of lower Medicine Bow age. In the Vermejo flora there are, to be sure, floral 

 elements that suggest an age slightly older than Laramie or lower Medicine Bow. 

 This is consistent with the upper Pierre rather than Fox Hills age assignment of 

 the Trinidad sandstone, which lies conformably below the Vermejo. On the other 

 hand, there are a number of Paleocene species in the Raton floras, suggesting that, 

 as in the case of the Denver-Dawson beds, the lower portion of the Raton formation 

 may be Cretaceous and the upper portion Paleocene and possibly younger. 



Fort JJnion flora — The extensive Fort Union flora of the Rocky Mountain 

 region is well known though in need of critical restudy, which is at present being 

 undertaken by Dr. Roland W. Brown of the U. S. Geological Survey. Knowlton ^ 

 regarded the Lance and Fort Union floras as essentially similar, a view which has 

 often been quoted in geological reports and textbooks. In view of the close rela- 

 tionship now estabUshed between the lower Lance and the lower Medicine Bow 

 floras, it is therefore surprising to find only two species in common between the 

 lower ]\Iedicine Bow and Fort Union floras. This somewhat anomalous situation 

 is in part explained by the discovery, as discussed under the Lance flora above, 

 that some of KnowIton's so-called Lance collections were obtained from strata now 

 conclusively known to be within the Fort Union formation. It has also become 

 apparent that the lower Lance (Hell Creek) flora is quite distinct from that of the 

 upper Lance (TuIIock and Ludlow) . The former is clearly of Laramie-Iower Medi- 

 cine Bow aspect, whereas the latter is more closely related to the flora of the Fort 

 Union. If this tentative observation is substantiated by further studies of the 

 Lance floras which I have already under way, it brings into harmony the evidence 

 of the plants and the vertebrates in placing the greatest faunal and floral break at 

 the end of lower Lance (Hell Creek) time.^ This is still not in agreement ■nath the 

 evidence afforded by marine invertebrates, since the Cannonball member of the 

 Lance, which overlies the Hell Creek member, has yielded a fauna which is said 



> Knowlton, F. H., U. S. Geol. Survey Prof. Paper 101, 223-349. 1917. 



«Knowlton. F. H., Washington Acad. Sci. Proc, vol. 11, 218-226, 1909; Bull. Geol. Soc. Am., vol. 25, 334, 1914; 

 U. S. Geol. Surv. Prof. Paper 155, 10, 1930. 



' Since the completion of this manuscript, collections have been made in the lower Lance formation {"Ceratops beds") 

 at its type locality. The fiora of about 75 species is closely related to the Medicine Bow and Laramie fioras and has little 

 in common with the TuIIock, Ludlow, and Fort Union floras. 



