Delfzyl, which was formerly an important fortress for the protection of the ancient sluices on the little river Delf (hence its name), has greatly benefited by the construction of the Ems (Eems) shipcanal connecting it with Groningen, and has a good harbour with a considerable import trade in wood.
As examples of class (i.) may be mentioned - erection or enlargement of buildings, laying down of permanent pasture, making of gardens or fences, planting of hops, embankments and sluices; as examples of (ii.) - chalking of land, clay burning, application to land of purchased artificial or purchased manure, except they have been made for the purpose of making provision to protect the holding from injury or deterioration.
Under ordinary conditions the sluices are raised to admit boats to pass from the half flood to half ebb, so that the river remains tidal up to Teddington, the next lock.
Long ditches with stone-paved sluices for washing this mineral-bearing material have long been used by the Indians, who also construct stone bars across the beds of the streams to make riffles and hold the deposited grains of gold.
The area south of this would be divided into four polders, with reservation, however, of a lake, Yselmeer, in the centre, whence branches would run to Ysel and the Zwolsche Diep, to Amsterdam, and, by sluices near Wieringen, to the northern part of the sea.