EUROPEAN METHODS OF OYSTER-CULTURE. 
371 
pass from the higher table-lands to the deeper North Sea, has cut wide and often deep 
channels bending between the islands. In all of these deeper areas are found oyster 
banks, sheltered as far as possible in the lee of seaward islands. Here the depth, 
normally between 10 and 30 feet, is sufficient to keep them covered with water even 
at the lowest spring tides. 
The location of oyster banks does not appear to be always, as figured by Mobius 
(Die Auster und die Austernwirthschaft, p. 5), on the steep-sloping side of a channel, 
but seems to be in every way similar in position to those examined by the writer at 
Cancale, Auray, and Arcachon, the banks being, in many instances, situated in the 
widened channel, often upon slightly elevated areas, the irregular limits of which can 
be determined by the sounding pole. The bottom, especially in the northern portion 
of the Watteumeer, is firm and stable, a mixture of sand, clay, and mud, and that 
it is in the main favorable for oyster growth is seen in the lines of natural oyster 
banks which form almost a diagram of the deeper waters. At points, however, as in 
the channels of Amrum and throughout the southernmost parts, muddy areas occur; 
these are soft, often shifting, and are naturally unproductive. The flats have excep- 
tionally shifting sands; they are in general hard and firm, readily sustaining the 
weight of a horse and cart. The rapidity with which the rise and fall of tide cover 
and uncover the extensive flats has been emphasized by Mobius as one of the unfavor- 
able conditions of the region, causing harmful accumulations of sediment and general 
shifting of sand and mud. On the other hand, it can hardly be doubted that the sedi- 
ments continually deposited from the landward shore, e . from the Husum Elver, would 
accumulate very seriously but for these currents. Where the outgoing currents are 
the strongest there apparently exist the most favorable conditions of bottom for the 
location of oyster banks, as Mobius has noted. 
The water conditions of the Wattenmeer are directly comparable to those of 
Arcachon in point of saltness, the normal density being about 1.021; this degree has 
already been noted as possessed by the chief centers of oyster-culture in France* 
and in Italy, especially in regions that have proven favorable for production, e. y., 
Auray, Arcachon, and Tarente. A table of densities prepared by the writer during 
his visit to the Wattenmeer shows, moreover, that the waters from Sylt down almost to 
the mouth of the Husum canal vary surprisingly little in density, even at different 
tides, the temperatures remaining almost uniform. This uniformity in the water 
density was not expected in view of the rapid filling and emptying of the basin, and 
is somewhat difficult to account for, suggesting a surprising regularity in the incoming 
volumes of freshened and salt water. It is noteworthy, perhaps, that the small 
freshened streams that contribute to reduce the density of the entire water volume 
appear to be distributed very evenly along the landward margin. 
The oyster banks number about fifty. Their length varies from a few hundred feet 
to a mile and a half, while the breadth averages hardly more than a few hundred feet. 
The exact position of each is accurately known by means of ranging sights, and the 
government, as will later be noted, examines their condition yearly and determines 
which are sufficiently rich to be dredged from. 
We may next briefly examine the way in which the oyster banks of the Watten- 
meer have been managed. They have certainly been retained in productive condition 
* See table of densities in U. S. F. C. Bulletin, 1890, p. 384. The densities were taken at about 
the same season of the year. The total difference in densities at various stations in the Wattenmeer 
during different tides (48 hours) is not greater than sp. gr. 0.001. 
