Here all the main drainage either runs northwards to the Gomal, passing through the uplands that lie west of the Suliman Range; or it gathers locally in narrow lateral valleys at the back of these mountains and then bursts directly eastwards through the limestone axis of the hills, making for the Indus by the shortest transverse route.
The coast is nowhere, however, very high, except at one or two points in Jutland, and at the eastern extremity of Moen, where limestone cliffs occur.
The northern and eastern regions are:broken by an extensive complex of chains and peaks, whose rugged limestone flanks are clad at most with stunted shrubs and barely leave room for a few precarious mule-tracks.
Nodular limestone (kankar) occurs in considerable deposits, and is used as road metal.
The whole region may be looked upon as formed by an arch or anticline of Carboniferous strata, the axis of which runs north and south; the centre has been worn away by erosion, so that the Coal Measures have been removed, and the underlying Millstone Grit and Carboniferous Limestone exposed to the influences which form scenery.
Coal, limestone and ironstone are mined.
The mineral occurs in metalliferous veins in the lead mines of Strontian in Argyllshire, Pateley Bridge in Yorkshire, Braunsdorf near Freiberg in Saxony; abundantly in veins in calcareous marl near Minster and Hamm in Westphalia; and in limestone at Schoharie in New York.
It usually occurs as lamellar or glanular masses, with a tin-white colour and metallic lustre, in limestone or in mineral veins often in association with ores of silver.
But more often worn to rolling downs; then the limestone range - writing-desk mountains that turn their steep fronts to the central snows; lastly low Cretaceous foothills, that sink softly into the steppe.
The southern edge of the county is formed by the scarps and moorlands of the Carboniferous Limestone and Millstone Grit (both of which form also the outlier of Pen-ceryg-calch north of Crickhowell), while the lowest beds of the Coal Measures of the South Wales coalfield are reached in the Tawe and Neath valleys (where the beds are much folded) and near Tredegar and Brynmawr.