ROCKY MOUNTAIN SUBREGION, a rather indefinite zoogeographical region em bracing the elevated area occupied by the Rocky Mountains, which zoologically presents certain Peculiarities very noticeable-n:0 a traveler from either the eastern lowlands or the Pacific Coast. The resemblance in the fauna is, indeed, rather to the East than to the West, as the Rockies do not form a zoological °divide° to anything like the extent which, the Sierra Nevada does, nor even as completely as does the fine of deserts which occupy the great depression of Nevada and Idaho between the Wahsatch Range and the Sierra Nevada. • A large number of species of animals. and plants extend from the Mississippi Valley to and throughout the Rocky Mountains, in forms which are • identical from one side of their wide range to the other, or which shade indistinguish ably from one varietal extreme in the East ,to another in the West. On the other hand the plants and animals common to both California and Colorado are comparatively few. The dry and foodless deserts of the Utah basin form a more potent barrier than the snows and altitude of either Sierras or 'Rockies. Thus the buffalo formerly wandered throughout the whole net work of interior valleys, and there is a special variety which seem never to have left the park pastures and scantily timbered defiles; yet Bear River, Utah, on the border of the alkali basin, is the farthest west they ever got south of northern Idaho. The elk, grizzly and bighorn, the mountain goat, white ptarmigan and certain other examples of animals, are common to both the Sierra Nevada and hie Rocky Mountain systems; but in all these cases they are species whose range extends far north where both lines of elevation converge in British Columbia. Yet the true vblacktail,p or Columbian deer, is never shot east of the' Cascades, nor does the Vir ginian, or willow deer, common enough the Rdelcies, wander over to the Cascades pr Sier ras of Oregon and California.
To a more limited extent the Great Plains on the east serve as a barrier between the com mingling of plants and anitnals indigenous to the mountains on the one hand and the Mis sissippi Valley on the other. And that this, as far as it goes, is a real barrier, is shown by the fact that many common weeds and trees, which flourish well in Colorado ,now, had never reached there until carried, either intentionally or accidentally by mah; that is, the place was suitable enough to them, but they had never been able to reach it.
The Rockies, then, form a zoogeographical district, which embraces practically the whole system of complicated chains from New Mexico to the borders of Alaska, and there is a curious •homogeneity throughout, a long list of insects, mollusks and animals of the lower classes, as well as of trees and herbs, occurring from the Rio Grande to the headwaters of the Saskatche wan, disregarding the difference in latitude, which in flat regions is the most powerful factor governing the distribution of animal and plant life.
This is not. exceptionally the case in the Rocky Mountains' alone, though here it is con spicuous and well-marked. It is true 'of the Ural-Carpathian system, of the Scandinavian ranges, of the Andes, of the great East-Afri can system, of which 'Mounts Kilimanjaro, Xenia and Gordon-Bennett are peaks; nor is it difficult of ' explanation. A great mountain province' is really a series of sub-provinces con centrically arranged, or, to put it in another way, heaped on top of one another, for the larjr est bound, embracing the whole extent of the mountains and their foothills, contains several more or less restricted areas, determined by alti tude, just as a vast lowland province, such as the whole eastern half of the continent, con tains several well-defined subdivisions according to zones of climate, succeeding one another from north to south. The cause of the natural division ,of these sub-provinces is precisely the same in both cases, for, whereas in the Missis sippi Valley the cooler or warner perature required by each animal or plant for its best development is obtained by moving to the north or to the south, so in a mountainous region too much cold or too much heat can be avoided by moving upward or downward, and climate varies with altitude instead of latitudes Hence, naturalists who have studied the mountains are able to mark out successive sub provinces, according to altitude, within the up per and lower borders of which certain forma of life are restricted, appearing neither below, or above, a limited number of thousand feet, ex cept as occasional wanderers. Botanists have long recognized this.