This hilly district contains the most productive land in the province, the soil consisting of diluvial drift or boulder clay.
The strata near the mountain chains and volcanoes consist of diluvial tuffs.
The northern part can best be regarded as a low plateau (once marine sediments) sloping southward, traversed by the large diluvial valleys of the Mississippi, Red and Ouachita rivers, and recut by smaller tributaries into smaller plateaus and rather uniform flat-topped hills.
The effect of this industry, however, is to lay bare a subsoil of diluvial sand which offers little inducement for subsequent cultivation.
In height) towards the north and north-west, and the soil is composed of diluvial sand, here and there mixed with gravel, but giving place to sea-clay along the western boundary and river-clay along the banks of the Maas and smaller rivers.
The country is also covered with thick diluvial and alluvial deposits containing gold.
The south-eastern portion of the province consists of high fen resting on diluvial sand.
All the rivers of this valley, flowing in deep beds of eroded diluvial tuffs, with a fall as much sometimes as 330 to 660 ft.
On the elevated parts of this large continent glaciers were formed, which, proceeding downwards to the lower levels, gave origin to large streams and rivers, the abundant deposits of which formed the diluvial sand and the diluvial clay.
Along the whole northern rim of Bosnia, as also in the fluvial and Karst valleys (poljes), are found diluvial and alluvial formations, interrupted at one place by an isolated granite layer.