The valleys of all these rivers, especially those of the Bulgarian and the Great Morava, and of the Nishava, contain considerable areas of level or low-lying country well suited for the growth of corn, and the low grounds along the Save and the Danube from the Drina to the Morava are also well adapted for agriculture, except the tract of fenland called the Machva, in the extreme north-west.
This is closely followed on the south-east by the Chalk country, occupying the whole of the rest of England except where the Tertiary Basins of London and Hampshire cover it, where the depression of the Fenland carries it out of sight, and where the lower rocks of the Weald break through it.
Formerly a great inlet with vague borders of lagoons and marshes, the Fenland has been reclaimed partly by natural processes, partly by engineering works patiently continued for centuries.
A comparison with other documentary evidence, however, leads to the identification of Holland with the forestum Merweda, or the bush-grown fenland lying between the Waal, the old Meuse and the Merwe.
This alteration of coast-line appears at Loosduinen, where the moor or fenland formerly developed behind the dunes now crops out on the shore amid the sand, being pressed to the compactness of lignite by the weight of the sand drifted over it.
The Fenland comprises a strip of Norfolk, a considerable part of Cambridgeshire, and the Holland district of Lincoln.