The marshy districts of Sologne, Brenne, Landes and Dombes still contain large undrained tracts.
The streets as originally laid out were wide and spacious, but being unpaved and undrained they were no better than mud tracks diversified by piles of garbage and foul-smelling stagnant pools.
There are undrained, swampy districts in Campeche, in the vicinity of the Terminos Lagoon, where malarial diseases are prevalent, and the same conditions prevail along the coast where mangrove swamps are found.
With a wet, undrained subsoil and a large population of Indians and half-breeds living in crowded quarters, the death-rate has been notoriously high, though the completion of the Valley drainage works in 1900, supplemented by underground sewers in the better parts of the city, and by better sanitation, have recently improved matters.
Nearer the Great Lakes the till sheets are trenched only by the narrow valleys of the large streams; marshy sloughs still occupy the faint depressions in the till plains, and the associated moraines have abundant small lakes in their undrained hollows: hence these drift sheets are of late Pleistocene origin.
As a whole the system forms the watershed between rivers flowing to the Indian Ocean - the Indus and its tributaries, Brahmaputra and its tributaries, and Salweenand the streams flowing into the undrained salt lakes to the north.
The old town is the upper or northern part, and is inhabited by the poorer classes, its streets being badly paved, crooked, undrained, dirty and pestilential.
It was once covered by the great Mojos Lake, and still contains large undrained areas, like that of Lake Rojoagua (or Roguaguado).
The thick peat moss or tundra of the undrained lowlands covers probably at least a quarter of Alaska; the ' The trees here grow as large as 10 in.