Whence came the native races of America? Doubtless the chain of Aleutian islands served as stepping-stones for straggling bands of Asiatics to cross over into continental Alaska many centuries ago; others may have traversed the ice-bridge of Bering's Strait; possibly prehistoric vessels from China, Japan, or the Malay peninsula were blown upon our shores by westerly hurricanes, or drifted hither upon the ocean currents of the Pacific. There are striking similarities between the flora on each shore of the North Pacific; and the Eskimos of North America, like the West-Slope Indians of South America, have been thought to exhibit physical resemblances to the Mongols and Malays. On the other hand, some archæologists hold that men as far advanced as the present Eskimos followed the retreating ice-cap of the last glacial epoch. In the absence of positive historical evidence, the origin of the native peoples of America is a mere matter of conjecture. Sidenote: Difficulties of colonization from the west. North America could not, in a primitive stage of the mechanic arts, have been developed by colonization on any considerable scale from the west, except in the face of difficulties almost insuperable. The Pacific coast of the country is dangerous to approach; steep precipices frequently come down to the shore, and the land everywhere rises rapidly from the sea, until not far inland the broad and mighty wall of the Cordilleran mountain system extends from north to south. That formidable barrier was not scaled by civilized men until modern times, when European settlement had already reached the Mississippi from the east, and science had stepped in to assist the explorers. At San Diego and San Francisco are the only natural harbors, although Puget Sound can be entered from the extreme north, and skilful improvements have in our day made a good harbor at the mouth of Columbia River. The rivers of the Pacific Slope for the most part come noisily tumbling down to the sea over great cliffs and through deep chasms, and cannot be utilized for progress far into the interior. Sidenotes: The Atlantic seaboard the natural approach to North America. The river system. The Appalachian valley system.