North America

The chief rivers that discharge to the Pacific rank below those that discharge to the Atlantic; but the Yukon, flowing from far ther Canada and inner Alaska, is one of the great rivers of the world. The Columbia, of hardly inferior rank, drains a large area of the Cordilleran system in Canada and the United States; it is peculiar in having one of its head branches rise at the eastern base of the Rocky mountains in Montana, so that its waters flow west ward through all the Cordilleran ranges of its latitude. The Colo rado discharges a muddy current into the Gulf of California.

Climate.

The climate of North America exhibits modifica tions of general conditions resulting from the globular form and eastward rotation of the earth. In January a mean temperature of zero or less invades the region north-west of Hudson bay, and extending as far south as the extreme central-northern United States, which thus resembles north-eastern Asia in departing greatly from the more temperate mean prevailing in similar lati tudes on the northern oceans. In July the great middle area of the continent becomes warmer than the oceans on the east and west, having a mean temperature ranging from 65° in the vicinity of the 50th parallel to above 80° south of the 35th parallel. Consequently the annual range between the means of January and July exceeds 40° for a large part of the continent, and exceeds 70° for much of the northern lands; the range of extreme tem peratures is much greater. On corresponding northern oceanic areas, the temperature range is little more than 20° ; and in the Southern Hemisphere it is probably less than o°.

The several members of the planetary wind system, including therein the trades of a broadened torrid zone, the prevailing and westerlies of middle latitudes, and the irregular winds of the polar region, are well exemplified over North America; but they are better seen in the drift of clouds than in the movements of the surface winds. In consequence of the dominance of westerly winds, a great stretch of the Pacific coast, even as far north as Alaska, has a small annual temperature range (generally less than 20°) ; while a range more appropriate to continental interiors is ex perienced over most of the eastern coast of the continent in tem perate latitudes ; hence the extraordinary unlikeness between the climates of western Europe and eastern North America, where habitable Great Britain faces almost uninhabitable Labrador. The

distribution of rainfall is likewise largely controlled by the general wind system. The West Indies, especially the mountainous islands, receive abundant precipitation from the passing trade winds. In Mexico and Guatemala the eastern slopes are for the most part better watered by the same winds (maximum, over loo in.) than the western slopes. Farther north the reverse holds true ; the Pa cific coast north of latitude 40° has an abundant rainfall (maxi mum over 10o in.), and its mountains are clothed with dense forests; but there are large areas of deficient rainfall (less than 20 in.) in the interior where the intermont and piedmont plains of the Cordilleras in middle latitudes are dry and treeless. Regions of heavy snowfall are chiefly in the far north-western Cordilleras: in the northern interior and Greenland it is less heavy.

Fauna and Flora.

The fauna of North America (Nearctic) is more closely related to that of Europe-Asia (Palaearctic) than to that of any other zoogeographical province; the two areas are united by many writers in one province (Holarctic). The rein deer (caribou), beaver and polar bear are found in both; the moose, wapiti, bison and grizzly bear of North America are closely related to the elk, red deer or stag, bison, and brown bear of Eurasia ; and the following groups are well represented in both provinces : cats, lynxes, weasels, bears, wolves, foxes, seals, hares, squirrels, marmots, lemmings, sheep, and deer. The following forms are characteristic of North America : (rodents) pouched rats or gophers, musk-rat, prairie dog, Canadian porcupine; (Carniv ora) raccoon and skunk ; (ungulates) musk ox, big-horn, Rocky mountain goat, prong-horn ; (marsupial) opossum. Among birds, there is a close resemblance to those of Eurasia, with some admix ture of South American forms, such as humming birds. Character istic forms are the Baltimore oriole, bobolink, cowbird, flycatchers, wood-warblers, California quail, tree grouse, sage grouse, wild tur key and turkey buzzard. Turtles are especially numerous ; sala manders are varied and large; rattlesnakes are among the reptiles.