52 FOSSIL FLORA OF THE SIEERA NEVADA. 



influences have left less irrefragable marks of their activity. The ves- 

 tiges of glacial action — moraines, erosions, striated rocks — are seen every- 

 where in the valleys of California; while the glacial drift on the eastern 

 slope of the United States scarcely passes south of the Ohio River. And 

 as the immense plains extending from the Missouri River to the base 

 of the Rocky Mountains have evidently been covered by water during 

 the prevalence of the terrace epoch, or after the glacial period, this bar- 

 rier, and also that of the chain of mountains still more impassable to 

 plants than to water, forcibly prevented a western redistribution of the 

 species destroyed in California by glacial agency. 



Notwithstanding these destructive influences, the flora of California still 

 preserves a few of the Pliocene types, and these, by their present habitat 

 and the apparent modifications of their characters, seem to point to what 

 have been the essential causes of the disappearance of the others. For 

 instance, Betula cequalis, Acer Bolanderi, Cercocarpus antiqwus, have now repre- 

 sentatives which seem to have been gradually dwarfed or modified by 

 the influence of the cold, and thus acclimatized gradually to the tempera- 

 ture of the subalpine zone which they now inhabit. Preserved during 

 the glacial period in some sheltered nook, they have thus apparently 

 wandered gradually to the mountains, following the disappearance of the 

 ice. A few other species have remained with their typical characters and 

 their habitat, — Castaneopsis chrysophylla and Cornns Kelloggii, for instance, 

 plants of hard texture and of great tenacity of life. According to the 

 data kindly furnished by Professor Bolander, these species inhabit now 

 near Oakland from an altitude of 1,800 feet to the Sierras, where Cas- 

 taneopsis chrysophylla is met with to an altitude of 8.000 feet. Very few, 

 if any, arborescent species of the present time have such a vertical 

 range of more than live thousand feet. Cornus Kelloggii, according to the 

 same authority, occupies the base of densely wooded slopes of the Sierras, 

 or is found in open places, where there is sufficient terrestrial moisture; 

 even in boggy places of the Yosemite Valley, ascending to 5,000 feet. 

 Another species, Cornus ovaUs, which was probably very abundant in the 

 Pliocene flora, has been about totally destroyed in California. It looks 

 like an isolated remnant of a type mostly driven southward at the glacial 

 period, and now inhabiting Mexico. The two species of Sequoia — one 

 the more predominant, the other the more remarkable, of the flora of 

 California — are evidently also remnants of the Pliocene. S. gigantea, which 



