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been reduced to any kind of scientific principles ; but is left entirely 
in the hands of the experienced though uneducated seaman. In 
these hands it is however of great importance ; as, in shallow seas 
and on coasting voyages, it supersedes entirely the scientific part of 
navigation, 
Two particulars are ascertained by the use of the sounding lead : 
the depth of water and nature of the bottom. It is to the latter 
only I shall call the attention of the Society. 
It is the opinion of many Geologists, that the bottom of the sea, 
being the receptacle of all the disintegrated particles of the land, 
must be an immense bed of alluvion, the parts of which, from the 
motion caused by tides or currents, must tend constantly towards the 
deeper portions of the ocean. 
It is evident, that the finer and lighter particles, which expose a 
greater surface in proportion to their gravity, are likely to be car- 
ried farthest ; so that near the shore we may expect to find gravels 
or shingle ; farther out sand; beyond that mud; and finally ooze 
or vegetable remains. In the same manner as in the beds of rivers, 
in the upper country, where the descent and consequently the velo- 
city is rapid, we have rocks and boulders; succeeded as we ap- 
proach the plains by gravel, sand ; then clay or mud; and, lastly, 
as the waters become sluggish and stagnant, by weeds and mosses. 
There can be no doubt, but, in heavy inshore winds, the waters 
which are propelled by the friction of the air on their surface to- 
wards the shore, must run off again by a subaqueous current known 
to seamen by the name of the “ undertow,” and that this is the 
chief cause of the abrasion of the shores. The velocity of this cur- 
rent will naturally diminish as it gets into deeper water; but may be 
very considerable even at great depths, as the following instance will 
show. 12 
