in the lowlands becomes too great under prevailing economic methods, do clearings and cabins begin to creep up the slopes.  Mountains are always regions of late occupation.  Even in the Stone Age, we find the long-headed race of Mediterranean stock, who originally populated Europe, distributed over the continent close up to the foot of the high Alps, but not in the mountains themselves, and only scantily represented in the Auvergne Plateau of France.  The inhospitable highlands of Switzerland, the German Alps, and the Auvergne received their first population later when the Alpine race began to occupy western Europe.[1187] The Mittelgebirge of Germany were not settled till the Middle Ages.  In the United States, the flood of population had spread westward by 1840 to the ninety-fifth meridian and the north-south course of the Missouri River; but out of this sea of settlement the Adirondack Mountains, a few scattered spots in the Appalachians, and the Ozark Highlands rose as so many islands of uninhabited wilderness, and they remain to-day areas of sparser population.  In 1800, the “bare spots” in the eastern mountains were more pronounced. [See map page 156.] Great stretches of the Rocky Mountains, of the Laurentian Highlands of Canada, like smaller patches in the Scandinavian and Swiss Alps, are practically uninhabited.

[Sidenote:  Mountains as transit regions.]

Mountain regions, like deserts and seas, become mere transit districts, which man traverses as quickly as possible.  Hence they often lie as great inert areas in the midst of active historical lands, and first appear upon the historical stage in minor roles, when they are wanted by the plains people as a passway to desirable regions beyond.  Then, as a rule, only their transit routes are secured, while the less accessible regions are ignored.  Caesar makes no mention of the Alps, except to state that he has crossed them, until some of the mountain tribes try to block the passage of Roman merchants or armies; then they become important enough to be conquered.  It was not till after the Cimbri in 102 B.C. invaded Italy by the Brenner route, that the Romans realized the value of Rhaetia (Tyrol) as a thoroughfare from Italy to Germany, and began its conquest in 36 B.C.  This was the same value which the Tyrol so long had for the old German Empire and later for Austria,—­merely to secure connection with the Po Valley.  The need of land communication with the Rhone Valley led the Romans to attack the Salyes, who inhabited the Maritime Alps, and after eighty years of war to force from them the concession of a narrow transit strip, twelve stadia or one and a half miles wide, for the purpose of making a road to Massilia.[1188] The necessity of controlling such transit lands has drawn British India into the occupation of mountain Baluchistan, Kashmir and Sikkim, just as it has caused the highlands of Afghanistan to figure actively in the expansion policy of both India and Russia.  The conquest of such transit lands has always been attended by road building, from the construction of the Roman highway through the Brenner Pass to the modern Russian military road through the Pass of Dariel across the Caucasus, and the yet more recent Indian railroad to Darjeeling, with the highway extension beyond to the Tibetan frontier through Himalayan Sikkim.