Among primitive tribes, who move in smaller groups and must conform closely to the dictates of their environment, the modifying effects of people and land through which they pass are conspicuous. Ratzel describes the gradual withdrawal of a Hottentot people from western Cape Colony far into the arid interior before the advance of Kaffirs and Europeans by saying: "The stock and name of the Namaquas wandered northward, acquiring new elements, and in course of time filling the old mold with new contents."[151] This is the typical result of such primitive movements. The migration of the Delaware Indians from an early home somewhere northwest of the Great Lakes to their historical habitat between the Hudson and Potomac Rivers was a slow progress, which somewhere brought them into contact with maize-growing tribes, and gave them their start in agriculture.[152] The transit lands through which these great race journeys pass exercise a modifying effect chiefly through their culture and their peoples, less through their physical features and climate. For that the stay of the visitants is generally too brief. [Sidenote: Effect of early maritime migration.] Even early maritime migrants did not keep their strains pure. The untried navigator sailing from island to headland, hugging the coast and putting ashore for water, came into contact with the natives. Cross currents of migration can be traced in Polynesian waters, where certain islands are nodal points which have given and received of races and culture through centuries of movement. The original white population of Uruguay differed widely from that of the other Spanish republics of South America. Its nucleus was a large immigration of Canary Islanders. These were descendants of Spaniards and the native Guanches of the Canaries, mingled also with Norman, Flemish and Moorish blood.[153] The Norse on their way to Iceland may have picked up a Celtic element in the islands north of Scotland; but from the Faroe group onward they found only empty Iceland and Greenland. This was an exceptional experience. Early navigation, owing to its limitations, purposely restricted itself to the known. Men voyaged where men had voyaged before and were to be found. Journeys into the untenanted parts of the world were rare. However, the probable eastward expansion of the Eskimo along the Arctic rim of North America belongs in this class, so that this northern folk has suffered no modification from contact with others, except where Alaska approaches Asia. [Sidenote: The transit land.]