LIO United States Survey of the Territories. [February, 
cisco; and (y) the Sierra Nevada flora, temperate, subalpine and 
alpine 
` 3. The Rocky Mountain region (in its widest sense extending 
from the Mississippi beyond its forest region to the Sierra Nevada), 
subdivisible into (a) a prarie flora, (£) a desert or saline flora, (y) a 
Rocky Mountain proper flora, temperate, subalpine, and alpine. - 
As above stated, the difference between the floras of the first 
.and second of these regions is specifically, and to a great extent 
generically, absolute; not a pine or oak, maple, elm, plane or 
irch of Eastern America extends to Western, and genera of 
thirty to fifty species are confined to each. The Rocky Mountain 
region again, though abundantly distinct from both, has a few ele- 
ments of the eastern region and still more of the western. 
Many interesting facts connected with the origin and distribu- 
tion of American plants, and the introduction of various types 
into the three regions, presented themselves to our observation or 
our minds during our wanderings. Many of these are suggestive 
of comparative study with the admirable results of Heer’s and 
Lesquereux’s investigations into the Pliocene and Miocene plants 
of the north temperate and frigid zones, and which had already 
engaged Dr. Gray’s attention, as may be found in his various pub- 
lications. No less interesting are the traces of the influence of a 
glacial and a warmer period in directing the course of migration 
of Arctic forms southward, and Mexican forms northward in the 
continent, and of the effects of the great body of water that occu- 
pied the whole saline region during (as it would appear) a glacial a 
period. e 4 
Lastly, curious information was obtained respecting the ages of 4 
not only the big trees of California, but of equally aged pines and 
junipers, which are proofs of that duration of existing conditions ) 
of climate for which evidence has hitherto been sought rather 
among fossil than among living organisms. 
Up to the year 1874 rumor had been telling many marvelous 
stories of strange and interesting habitations of a forgotten people, 
who once occupied the country about the headwaters of the Rio — 
San Juan, but these narrations were so interwoven with romance a 
that but few people placed much reliance upon them. To those- 
well versed in archeology, ruins of an extensive and interesting 
character were known to éxist throughout New Mexico and Ari- - 
zona, and the various reports of Abert, Johnson, Sitgreaves, Simp” 
son, Whipple, Newberry, and others form our most interesting , : 
chapter in ancient American history; but their researches, asid 
from the meager accounts published by Newberry, throw no light 
on the marvelous cliff dwellings and towns north of the San Juan- 
In 1874 the photographic division of the United States Geologi 
