The geographical environment of a people may be such as to segregate them from others, and thereby to preserve or even intensify their natural characteristics; or it may expose them to extraneous influences, to an infusion of new blood and new ideas, till their peculiarities are toned down, their distinctive features of dialect or national dress or provincial customs eliminated, and the people as a whole approach to the composite type of civilized humanity. A land shut off by mountains or sea from the rest of the world tends to develop a homogeneous people, since it limits or prevents the intrusion of foreign elements; or when once these are introduced, it encourages their rapid assimilation by the strongly interactive life of a confined locality. Therefore large or remote islands are, as a rule, distinguished by the unity of their inhabitants in point of civilization and race characteristics. Witness Great Britain, Ireland, Japan, Iceland, as also Australia and New Zealand at the time of their discovery. The highlands of the Southern Appalachians, which form the "mountain backyards" of Kentucky, Tennessee and North Carolina, are peopled by the purest English stock in the United States, descendants of the backwoodsmen of the late eighteenth century. Difficulty of access and lack of arable land have combined to discourage immigration. In consequence, foreign elements, including the elsewhere ubiquitous negro, are wanting, except along the few railroads which in recent years have penetrated this country. Here survive an eighteenth century English, Christmas celebrated on Twelfth Night, the spinning wheel, and a belief in Joshua's power to arrest the course of the sun.[75] An easily accessible land is geographically hospitable to all new-comers, facilitates the mingling of peoples, the exchange of commodities and ideas. The amalgamation of races in such regions depends upon the similarity or diversity of the ethnic elements and the duration of the common occupation. The broad, open valley of the Danube from the Black Sea to Vienna contains a bizarre mixture of several stocks--Turks, Bulgarians, various families of pure Slavs, Roumanians, Hungarians, and Germans. These elements are too diverse and their occupation of the valley too recent for amalgamation to have advanced very far as yet. The maritime plain and open river valleys of northern France show a complete fusion of the native Celts with the Saxons, Franks, and Normans who have successively drifted into the region, just as the Teutonic and scanter Slav elements have blended in the Baltic plains from the Elbe to the Vistula. [Sidenote: Change of habitat.]