Recent History of the Rocky Mountain Flora. 241 
The flora resembles therefore, as the tables show above, more that of the 
region of the Great Lakes than that of the Rockies'). 
Recent History of the Rocky Mountain Flora. The Stony Mountains a 
well-marked group by the head waters of the Missouri on the east, and the 
head waters of the Snake and Columbia rivers on the west, and the Park 
Mountains in southern Wyoming, central Colorado, and northern New 
Mexico, together constitute the Rocky Mountain system. The Stony 
Mountains are of diverse structure. There are a number of great ranges not 
systematically grouped, complicated by volcanic mountains, plateaus and hills. 
The ranges are moderately high; and by reason of the northern altitude and 
a fair amount of rainfall, they are covered for many months with snow, and 
here many beautiful streams have their origin. The flanks of the mountains 
and high plateaus are often covered with great forests, and the low foot hills 
with gnarled trees. 
The ranges of the Park Mountains are more irregular than those of the 
Stony Mountains, and have a general north- and-south trend. Between the 
ranges are great valleys known as parks. The four most important are the 
North, Middle, South and San Luis parks. Above the timber line, the peaks 
are naked; below on the flanks of the mountains great forests stand, and often 
spread over elevated plateaus while the valleys are beautiful prairies, or parks. 
The central portions of the ranges are in the main composed of metamorphic 
rocks of great age. On the flanks of the mountains and out in the parks 
there are many beds of volcanic rocks which serve still further to modify the 
aspect of the ranges. In a few cases, especially on the western side, these 
volcanic beds have been piled up in mountain forms’). 
The history of region, as it has influenced the distribution of plants, is 
briefly, as follows: At the close of the Jurassic the first great upheavals took 
place®). Two lofty ranges of mountains — the Sierra Nevada and the Wahsatch 
were pushed up from the great subsiding area. These movements were fol- 
lowed by a prolonged subsidence during which Cretaceous sediments accumul- 
ated over the Rocky Mountain region to a depth of 9000 feet or more. Then 
came another vast uplift whereby the Cretaceous sediments were elevated into 
the crests of mountains, and a para ast-range was formed fronting the _ 
Pacific. The Rocky Mountains, with Bo table-land from which theys._ 
rise were permanently raised above the sea. The slopes of the land were 
clothed with an abundant vegetation, in which we may trace the ancestors of 
many of the living trees of North America. Vast lakes existed among the 
mountains, and the climate as proved by the presence of the lakes must 
have been much more humid than at present in the same region, and more 
ı) RypBeErs, P. A.: Flora of the Black Hills of South Dakota. Contributions from the U. S$. 
National Herbarium III: 463—478. June 1896, 
2) PowELL, J. W.: Physiographic Regions of the United States. National Geographic Mono- 
graphs I, No. 3: 87—88. ö 
3) GEIKIE, Sır ARCHIBALD: Text Book of Geology. Third ed. 1893: 1078. 
Harshberger, Survey N.-America, 16 
