46 
of thesoundings, and have formed tables of these: for the use of 
navigators; but their modes of description are so vague, that it is 
difficult to reconcile them, and hence an opinion has arisen among 
many, that this kind of knowledge is not to be depended on. 
The portion of the ocean adjacent to the mouth of the channel, 
being so much traversed by the maritime nations, has been rather 
minutely explored; and the bank of soundings, or that space 
wherein the sea is less than 100 fathoms in depth, and which is 
nearly confined within a line drawn from Bourdeaux to the west of 
Treland, has been delinéated both by French and English Hydro- 
graphers, 
This line, or the edge of the bank, is about 200 miles to the 
west of the Land’s end of Cornwall; for the last 150 miles, the 
ground is almost flat; but, beyond that line, the inclination of the 
bottom rapidly changes, and the depth suddenly increases to 200 
fathoms and upwards. Round the bottom of the bay of Biscay, 
this depth is found within a few miles of the shore. 
On so extensive and level a plain, it would be unreasonable to 
expect the bottom to be entirely composed of alluvion from distant 
lands. The action of the ebbing and flowing tide must nearly be 
the same each way ; and, although it may have the effect of grind- 
ing or wearing down the upper surface of the strata into small frag- 
ments or fine sand, yet it cannot transport them far from the place 
where they are produced. 
~ In fact, we find that the pilots, although their notes are inserted 
only in detached places, ascribe a uniformity of character to con- 
siderable portions of the bottom ; showing distinctly, that, like the 
soils on the dry land, this character must derive its origin from the 
nature of the subjacent rock, by the disintegration of which these 
soils are formed. 
