FOSSIL FLOBA. 785 



lava flows, rest in many places upon the upturned edges of Archean and 

 Paleozoic rocks. In most instances the basic breccias either rest directly 

 upon the acid rocks or else the underlying rocks are not exposed. The 

 acid breccias are found on both banks of the Yellowstone River near the 

 mouth of Elk Creek, and near the junction of the Yellowstone River 

 with Hellroaring Creek, as well as on Crescent Hill and near the head 

 of Tower Creek. 



In the neighborhood of Lost Creek, and on the northern end of 

 Specimen Ridge, along the drainage of Crystal Creek, the basic breccias 

 are known to lie directly upon the acid breccias. In these localities the 

 fio.ra has a character distinctly its own, and bears evidence of being younger 

 than the flora from the acid breccias. The basic series of rocks is typified 

 at the Fossil Forest, and also at the cliff a. short distance to the south and 

 east of the Fossil Forest. They occur also on the east bank of Lamar 

 River, between Cache and Calfee creeks. All of these localities are char- 

 acterized by their plant remains, and the following determinations of age 

 are fully warranted. 



The table of distribution of Tertiary plants in the Yellowstone National 

 Park has been prepared for the purpose of showing in a graphic manner 

 the distribution of the various plants within the limits of the Park and the 

 affinities of those having an outside distribution. From this it appears that 

 the Tertiary flora consists of 150 more or less satisfactory species. Of 

 this number, 81 species, or over 50 per cent, are here described for the first 

 time. New species can not, of course, have the value in determining age. 

 that previously described forms have, but when their general facies as well 

 as close affinities are taken into account, they also become of positive value. 

 On eliminating the 81 new species, together with 8 forms not specifically 

 named, there remain 61 species upon which we must depend in the deter- 

 mination of the ages of the various strata in which they are contained. 



A further examination of the table brings out the fact that this flora 

 may be naturally divided into 3 more or less distinct subfloras or stages. 

 These three divisions are the older or acid series, the intermediate series, 

 and the basic or younger series. The first division (acid) has a flora of 79 1 

 species; the second (intermediate) a flora of 30 species, and the third (basic) 

 a flora of 70 species. It further appears that 23 species or forms are 

 common to two or more of the divisions. 



MON XXXII, PT II 50 



