Its principal streams are those that cross the West Shore of the Coastal Plain and here wind their way from Parr's Ridge rapidly toward the south-east in narrow steep-sided gorges through broad limestone valleys.
The Alleghany Plateau consists of nearly horizontal beds of limestone, sandstone and shales, including important seams of coal; inclines slightly toward the north-west, and is intricately dissected by extensively branching streams into a maze of narrow canyons and steep-sided hills.
The various ridges and mountain masses are separated by steep-sided valleys, which run down to the sea, forming deep fjords, so that no part of the interior is more than 12 m.
On its east, between it and the coast, which it follows at a moderate distance, is a fertile strip difficult of access, and on the west it throws off so many lateral ranges and spurs, as to break up the country into a chaos of corrugated and precipitous hills and steep-sided valleys, each with a rapid perennial stream.
Instead of wide, barren, wind-swept valleys, here are found fertile alluvial plains - such as Manipur - but for the most part the erosive action of the river has been able to keep pace with the rise of the river bed, and we have deep, steep-sided valleys eating their way northwards owing to the greater rainfall on the southern than on the northern slopes.