Exceptions to this rule are found in barren or inaccessible coasts like the Pacific littoral of Peru and Mexico, and on shores like those of California, western Africa and eastern Luzon, which occupy an adverse geographic location facing a neighborless expanse of ocean and remote from the world's earlier foci of civilization. Therefore the descent from the equatorial plateau of Africa down to the Atlantic littoral means a drop in culture also, because the various elements of civilization which for ages have uninterruptedly filtered into Sudan from the Mediterranean and the Red Sea, have rarely penetrated to the western rim of the highland, and hence never reached the coast. Moreover, this steaming lowland, from the Senegal River to the Kamerun Mountains, has been a last asylum for dislodged tribes who have been driven out by expanding peoples of the plateau. They have descended in their flight upon the original coast dwellers, adding to the general condition of political disruption, multiplying the number of small weak tribes, increasing the occasions for intertribal wars, and furthering the prevailing degradation. The seaboard lowlands of Sierra Leone, Liberia and the Ivory Coast have all suffered thus In historic times.[516] All this region was the original home of the low, typical "Guinea Nigger" of the Southern plantation. The coasts of Oregon and California showed a parallel to this in their fragmentary native tribes of retarded development, whose level of culture, low at best, sank rapidly from the interior toward the seaboard. They seem to have been intruders from the central highlands, who further deteriorated in their weakness and isolation after reaching the coast. They bore every mark of degradation in their short stature, linguistic and tribal dismemberment, their low morals and culture, which ranked them little above the brutes. In contrast, all the large and superior Indian groups of North America belonged to the interior of the continent.[517] [Sidenote: Cultural contrast of coast and interior.] The long, indented coast of the Mediterranean has in all ages up to modern times presented the contrast of a littoral more advanced in civilization than the inland districts. The only exception was ancient Egypt before Psammeticus began to exploit his mud-choked seaboard. This contrast was apparent, not only wherever Phoenicians or Greeks had appropriated the remote coast of an alien and retarded people, but even in near-by Thrace the savage habits of the interior tribes were softened only where these dwelt in close proximity to the Ionian colonies along the coast, a fact as noticeable in the time of Tacitus as in that of Herodotus five hundred years before.[518] The ancient philosophers of Greece were awake to the deep-rooted differences between an inland and a maritime city, especially in respect to receptivity of ideas, activity of intellect, and affinity for culture.[519]