SHORTER GONTRIRUTIONS TO GENERAL GEOLOGY, 1919. 



AN EOCENE FLORA FROM TRANS-PECOS TEXAS. 



By Edward Wilber Beery. 



INTRODUCTION. 



During the fall of 1916 I received a small 

 collection of fossil plants which had been ob- 

 tained during a geologic reconnaissance of the 

 trans-Pecos region of Texas, by Charles Law- 

 rence Baker. A prelirainary report was sent 

 to Mr. Baker in November of that year and 

 was quoted in his discussion of the geology 

 of that region.^ I have since made a careful 

 study of the collection, and although it con- 

 tains only a few species the occurrence of fossil 

 plants in this region is worthy of more definite 

 and detailed record, especially as these plants 

 enabled me to assign a definite age to the begin- 

 ning of the igneous activity of the region and 

 to establish correlations between the floras of 

 the Mississippi embayment and the Rocky 

 Mountain region. 



A general accomat of the geology is contained 

 in a recent paper by Baker and Bowman, al- 

 ready cited. The fossil plants, which are 

 described in the following pages, were found 

 in the basal tuffs of the Barilla Mountains be- 

 tween 10 and 15 miles south of Toyahvale and 

 not far east of the main road from Toyah to 

 Fort Davis. These tuffs are rhyolitic and not 

 andesitic like those of the Denver Basin, which 

 contain what appears to have been a contem- 

 poraneous flora, and they overlie imconforma- 

 bly beds which are of Pierre (Cretaceous) age, 

 according to Baker and Bowman's determina- 

 tion of the geology. 



One is tempted to assign all of what might 

 be called the Laramide epoch of igneous activ- 

 ity along the Rocky Mountain front to the 

 early Tertiary. There certainly appears to 



1 Baker, C. L., and Bowman, "VV. F., Geologic exploration of the south- 

 eastern front range of trans-Pecos Texas: Texas XJniv. Bull. 1753, pp. 

 123-124, 1917. 



have been sjoichroneity of inception of vol- 

 canism in the Denver, Raton Mesa, and Barilla 

 Mountain regions, although farther north, in 

 Montana, this activity appears to have com- 

 menced at an earlier date. Rhyolitic lavas 

 overlie the coal-bearing San Carlos formation, 

 which is of Upper Cretaceous age, and are pres- 

 ent also in the Sierra Vieja of Texas. ^ The 

 basalts and phonolites of Uvalde and Travis 

 counties intrude the Taylor marl (Upper Cre- 

 taceous) and are commonly considered to be 

 of Tertiary age. Ash beds are also known to 

 occur in the Texas Coastal Plain in late Eocene 

 rocks, while on the other hand Udden reports 

 volcanic tuffs in the Chisos country which are 

 said to be interbedded in rocks of Navarro 

 (Upper Oetaceous) age. It appears evident 

 that no reliance can be placed upon the vol- 

 canism as furnishing even an approximate 

 datum plane for correlation, although it seems 

 to be established that the Cordilleran orogenesis 

 of the Tertiary was accompanied by volcanic 

 activity on a grand scale. 



ENVIRONMENTAL CONDITIONS INDICATED BY 

 THE FLORA. 



The flora here described was found about 

 340 miles west of the most westerly known 

 outcrop containing fossil plants of Wilcox 

 (lower Eocene) age, which is on Calaveras 

 Creek in Wilson County, Tex.; 355 miles west 

 of the most westerly known outcrop containing 

 supposed Midway (Eocene) plants; 500 miles 

 almost due south of the Raton Mesa country, 

 in southeastern Colorado and northeastern 

 New Mexico, which yields the flora of the 

 Raton formation; and 670 miles south of the 



2 Vaughan, T. W., Reconnaissance in the Rio Grande coal fields of 

 Texas: XJ. S. Geol. Survey Bull. 164, pp. 76-83, 1900. 



