528 F. H. KKOWLTON EVOLUTION OP GEOLOGIC CLIMATES 



America that militates fatally against the conclusion that they reqnireci 

 at least a warm temperate and possibly a subtropical climate. Turning 

 to the Eocky Mountain region we may select the Frontier formation (of 

 Colorado age), concerning which Knowlton ^® has published as follows; 



"The climate during Frontier time appears to liave been tropical or sub- 

 tropical, as is shown in a number of ways. Thus, one of the most abundant 

 of the ferns (Tapeinidium) was indeterminate in growth, a condition that 

 could survive to the extent here indicated only in the absence of frosts. The 

 most abundant elements in this flora are the ferns, . . . and all call for a 

 tropical or subtropical habitat. . . . The wax-berry (Myrica), the oak 

 (Quercus), and the willow (Salix), might not be out of place in a tropical 

 region, but the figs (Ficus) and the cinnamon trees (Cinnamomum) certainly 

 required a tropical or subtropical location." 



The flora of the Vermejo formation (of Montana age) includes bread- 

 fruit trees, 16 species of figs, fan palms of gigantic size as well as types- 

 indicating a more temperate condition, but when viewed as a whole the 

 following conclusion was reached : ^^ 



"From the abundance and proportions of the plant types it may be presumed 

 that there was an abundance of moisture, from the absence of marked growth 

 rings that there was no sharp differentiation of seasons, and from the general 

 facies of the whole flora that the climate was warm temperate and perhaps- 

 even subtropical." 



Tertiary floras. — Origin of herbaceous types of vegetation. — Before 

 discussing the various Tertiary floras it is important to call attention to- 

 a very profound change that came about in plant life at this time — 

 namely, the evolution of herbaceous types of vegetation. During the- 

 whole of the Cretaceous and at least the earlier part of the Tertiary herbs- 

 are practically unknown, whereas in the present flora they vastly out- 

 number the woody types in all the cooler parts of the world. It seem.s 

 to be generally accepted that the herbs have descended from woody plants- 

 in direct response to increasing refrigeration during Tertiary time. 

 Dr. E. W. Sinnott ^^ has recently published a very important article on 

 "The evolution of herbs,'^ from which I venture to quote the following: 



"These facts — that woody plants are more ancient than herbs is shown by 

 evidence from fossils, from natural relationships and from anatomy; that 

 herbs are now dominant and woody plants few in species in regions subject 

 to low winter temperatures, and vice vei'sa; that regions which have been 

 isolated from the north temperate land-mass possess few herbs in the ancient 



" F. H. Knowlton : U. S. Geol. Survey Prof. Paper 108, 1017, p. 79. 

 " F. H. Knowlton : U. S. Geol. Survey Prof. Paper 101, 1917, p. 235. 

 18 Ee W. Sinnott : Science, new ser., vol. 44, 1916, p. 295. 



