AN EOCENE FLORA EKOM TRANS-PECOS TEXAS. 



ous species of holly are confined to the south- 

 eastern part of the coiintry, and several reach 

 their western limits in east or central Texas. 

 The occurrence in the Barilla Mountains is 

 therefore slightly beyond the normal western 

 limit of range of the existing North American 

 hollies, but as several species occur in the 

 Tertiary floras of the Rocky Mountain province 

 this occurrence is without any special signifi- 

 cance. 



Summarizing the indications afi^orded by the 

 different species of plants found as fossils in the 

 basal tuffs of the Barilla Mountains we may 

 legitunately conclude that they point to warm 

 temperate climatic conditions with abundant 

 precipitation and a plentiful supply of ground 

 water. The actual temperatures can not be 

 estimated, but hard winters may be regarded 

 as very improbable, and there is nothing to 

 indicate that mild winters such as occur at the 

 present time in the Coastal Plain portions of 

 the Carolinas and Georgia would have been 

 prohibitive to the existence of the plants found 

 in these tuffs. We may therefore picture the 

 climatic conditions of trans-Pecos Texas during 

 the period in which these plants flourished as 

 corresponding to those fomid at the present 

 time in the Coastal Plain portion of South 

 Carolina. 



AGE OF THE FLORA. 



Although the determined forms are but six 

 in number and two of the six are new to science, 

 it is possible to reach somewhat definite con- 

 clusions regarding the age of the flora. In a 

 subsequent paragraph the question of the exact 

 horizon in the Eocene to which this flora 

 should be referred is considered, but it may be 

 noted here that the four species which occur 

 outside of the Barilla Mountains are all found 

 in the early Eocene of the Rocky Mountain 

 province or in the corresponding beds of the 

 Atlantic Coastal Plain, and on the other hand 

 none of these forms are certainly foimd in the 

 Upper Cretaceous of these or any other areas. 

 It is true that Asimina eocenica has been re- 

 corded from the Montana group, but as I 

 pointed out in discussing the presence of this 

 species in the Midway ( ?) flora of Texas, ^ the 

 Upper Cretaceous material referred to this 

 form is not identical with it, nor is it even 

 referable to the genus Asimina, which is not 

 yet known from the Upper Cretaceous. 



1 Berry, E. W., U. S. Geol. Survey Prof. Paper 91, p. 14, 1916. 



Similarly palm remains identified as those of 

 Sabalites grayanus have been reported from the 

 Upper Cretaceous of the Western States. 

 Sabalites is, however, a form genus for fossil fan 

 palms whose generic affinity is not certainly 

 known, and it is thus without significance in the 

 present connection, even if there were any ade- 

 quate gromid for identifying the western 

 material as Sabalites grayanus, which there is 

 not. 



Another criterion in evaluating the present 

 flora is furnished by the absence from it of cer- 

 tain elements. Although negative evidence is 

 rightly considered of less value than positive 

 evidence, it remains true that the types of 

 plants that are most successful in resistmg de- 

 cay and those that almost invariably survive 

 maceration and thus become fossilized in a 

 recognizable form when they are at aU common 

 in any region are the gymnosperms. The 

 Mesozoic has frequently been termed the age of 

 gmynosperms or the age of conifers, from the 

 preponderance of the remains of those plants in 

 the floras of that era, and a considerable pro- 

 portion of the older Mesozoic types survived 

 tliroughout Upper Cretaceous time. These in- 

 clude the important genera Sequoia, Geinitzia, 

 Araucaria, Widdringtonites, BracliyphyUum, 

 Baiera, CzeJcanowsl'ia, Moriconia, Androvettia, 

 TTiuites, and numerous others. Fragments of 

 leafy twigs or cone scales are present in many 

 coarse deposits in which all the other vegetable 

 material has been reduced to imrecognizable 

 debris. There are no traces of gymnosperms 

 in the plant remains found m the basal tuffs of 

 the Barilla Mountains, and from this negative 

 evidence, which must be regarded as of consid- 

 erable importance, I conclude that the age of 

 these tuffs must be post-Cretaceous. 



The genus Geonomites is distinctly a Tertiary 

 type, for here again, notwithstanding the fact 

 that species of Geonomites have been reported 

 from the Upper Cretaceous of southwestern 

 Texas, I have aU the collected material and can 

 state positively that Geonomites has never been 

 found in the Upper Cretaceous deposits, the 

 specimens that have been identified as repre- 

 senting this genus being obviously those of fan 

 palms and not feather palms. The other three 

 genera represented in the flora from the tuffs 

 of the Barilla Mountains — Ilex, Juglans, and 

 Oreodaphne — are all genera with a known Upper 

 Cretaceous ancestry and are commonly found 

 among Upper Cretaceous collections of plants. 



