188 CONCHOLOGIST’S COMPANION. 
it is impossible to become so accurately acquainted, 
from the nature of the element in which they sub- 
sist. We are, however, fully warranted in concluding, 
from well-known facts, and recent observations, that 
were it not for their incessant labours, those mighty 
rivers, 
‘« To whose dread expanse, 
Continuous depth, and wondrous length of course, 
Our floods are rills,’’ 
would, in time, become impeded by the vegetable 
masses, and innumerable trunks, and branches, of 
large forest trees, which are continually carried into 
them by adventitious causes ; and that a considerable 
proportion of these, from the preservative nature of 
salt-water, would otherwise, probably, last for ages, 
form a basis for fresh accumulations, and eventually 
become productive of evils, of the extent of which, 
in the present harmonious and admirably balanced 
state of things, it is impossible to form an adequate 
conception. 
Nor is this all. The feeble Teredines open a source 
of considerable riches to the inhabitants of Sweden, and 
to those persons who reside on the borders of the White 
Sea, by employing the vigilance of the Dutch. The 
necessity which they impose upon these active people, 
of continually tarring and repairing their dikes and 
vessels, forms a bond of union between these two com- 
