GENERAL CONCLUSIONS. 53 



in all probability covered the higher slopes of the mountains of that epoch, 

 has been destroyed everywhere, except in some deep valleys surrounded 

 with walls of high granitic peaks, where it stands as a wonder of the 

 vegetation of this continent. The other, >S'. sempervirens, left here and 

 there, has again taken the ascendency under more favorable physical 

 circumstances. Its present distribution explains its preservation until the 

 present epoch. According to Professor Bolander, " the distribution of the 

 Redwood depends upon sandstone and oceanic fogs. Where either one 

 of these conditions is wanting there is no Redwood. The Redwoods 

 begin in the northern part of Monterey County, in isolated groups, in 

 deep, moist canons. A short distance south of Monterey City, on the 

 .Monterey Bay, a white bituminous slate sets in, and extends nearly to 

 Pajaro River. On this no Redwood is found but Pinus iu^it/ui*. At Pajaro 

 River, eight to ten miles from the ocean, they set in again, and extend 

 to nearly twenty-eight miles south of this city (San Francisco), either in 

 deep canons, or in groves extending over several ridges eastward as far 

 as the fog may reach. Thus they continue in similar localities to latitude 

 42°, the State boundary." 



From these facts, as also from what is known of the general distribu- 

 tion of Conifers, generally depending on a high degree of atmospheric 

 moisture, the character of the flora of the Chalk Bluffs indicates the geo- 

 graphical station of the localities where the Pliocene plants have been 

 found, as that of a region sheltered by ranges of mountains against the 

 influence of the Pacilic fogs, and whose vegetation has been influenced 

 by circumstances analogous to those governing it, as at the present 

 time. 



The plants described here from the Pliocene clearly expose the climate 

 of the period which they represent. They record a temperature a few 

 degrees higher, in the average, than that of Middle California, or, like the 

 species of the Chalk Bluffs of the Mississippi, they represent a latitude 

 of a few degrees farther south. The Palms were very rare in this flora ; 

 only a single specimen of a Sabal is found in the whole collection. 

 Nevada County is on the 39th parallel of latitude, and a species of Palm 

 still inhabits California under the 34th degree. For the Mississippi Valley, 

 Sabal and Chamcerops species have their northern limits also under this 

 same latitude. The action of a warmer climate seems indicated by the 

 Oaks of the Mexican type, and bv species of Ficus ; hut this is counter- 



