The southern ranges revert again to the northwest to southeast trend lines characteristic of the Dinaric Alps. They are, however, more gentle and accessible than the serpentine zone, the eastern highlands, or the North Albanian Alps. Transition to the lowlands is less abrupt, and arable valley floors are wider. Limestone is predominant, contributing to the cliffs and clear water along the Albanian Riviera. An intermixture of softer rocks has eroded and become the basis for the sedimentation that has resulted in wider valleys between the ridges than are common in the remainder of the country. This terrain encouraged the development of larger landholdings, thus influencing the social structure of the area (see ch. 5, Social System). [Illustration: Source: Adapted from Norman J. G. Pounds, _Eastern Europe_, Chicago, 1969, p. 824. _Figure 2. Landform Regions in Albania_] Lowlands A low coastal belt extends from the northern boundary southward to about Vlore. It averages less than ten miles deep but widens to about thirty miles in the Elbasan area. In its natural state it is characterized by low scrub vegetation, varying from barren to dense. There are large areas of marshland and other areas of bare eroded badlands. Where elevations rise slightly and precipitation is regular--in the foothills of the central uplands, for example--the land is excellent. Marginal land is being reclaimed wherever irrigation is possible. The land itself is of recent geological origin. It has been, and is being, created by sediments from the many torrents that erode the interior mountains. New alluvial deposits tend to be gravelly, without humus, and require many years before sufficient vegetation to make them fertile can be established. The sedimentation process, moreover, raises river channels above the level of the nearby terrain. Channels change frequently, devastating areas that have not been stabilized and creating marshes in others by blocking off the drainage. Road builders are confronted with difficult and constantly changing conditions. Rainfall is heavy during the winter and is infrequent to nonexistent during nearly half the year. Mosquitoes thrive in the hot, humid, and marshy land. Only since about 1930 have there been effective measures to control malaria. Before then no extensive working of areas near the marshes could be seriously considered. For these reasons the coastal zone, in addition to supporting few people, has until relatively recently acted as a barrier, hindering, rather than encouraging, contact with the interior.