Along the northern coast, almost every district has its principal river, and most of them are navigable up to the maritime capitals for native vessels of considerable burthen; but they all have the disadvantage of being partially blocked up at their discharge by extensive bars and mud banks, an evil which is extending with the increase of agriculture, by reason of the quantify of soil necessarily washed down in the process of irrigating the land for the rice cultivation. Most of them require the application of jetties or piers to deepen the passages at their entrance. There are no lakes of any considerable size on Java, for that name cannot be given to the _ráwas_, or swamps, which though swelled to a considerable size in the wet season, are for the rest of the year either dried up or choked by vegetation. Of this description are two extensive tracts; one inland of _Japára_, usually termed by the Dutch the _Binnen Zee_, or inland sea; and another in the district of _Semárang_. In _Báglen_ also (one of the native provinces on the southern side of the island) there is a lake which supplies the neighbouring country with fish, and along the coast of which a traffic is carried on in boats. Extensive swamps are also found in some parts of the native provinces, and in the mountainous districts of the _Súnda_ country. Several very beautiful lakes, of small dimensions, are discovered among the hills, and some of them can evidently be shown to have been formed of the craters of extinct volcanos. The general aspect of Java on the northern coast is low, in many places swampy and overgrown with mangrove trees and bushes, particularly towards the west. The southern coast, on the contrary, consists almost entirely of a series of rocks and cliffs, which rise perpendicularly to a considerable height. In the interior, stupendous mountains stretch longitudinally throughout the island, while others of an inferior elevation, and innumerable ranges of hills running in various directions, serve to form and confine plains and valleys of various elevations and extent. On the northern side, the ascent is in general very gradual, from the sea-coast to the immediate base of the mountains; particularly in the western parts of the island, where it has the greatest breadth, and where the mountains are situated far inland. In approaching the mountains, which lie at the back of Batavia, there is a gradual but almost imperceptible acclivity for about forty miles. In other parts, where the mountains and hills approach nearer to the coast, the ascent is of course more abrupt, as may be observed in the vicinity of _Semárang_.