44 
by the surface, occasions less action against the bottom during the 
ébb. But, as we pass off towards the ocean, we are presented with 
phenomena of a different kind. 
To the south of the bay of Dublin, along our shores, are the re- 
markable banks called the Irish grounds. ‘They have never yet 
been sufficiently explored ; and I was called off to the west of Ire- 
land last year, when about to begin that survey. I am however 
strongly inclined to think these banks will be found, not merely ac- 
cumulations of sand, but to be in fact owing to the existence of 
ridges of rock or other solid matter in that situation ; the more espe- 
cially as the rough bottom extends from thence all the way over to 
Carnarvonshire. 
To the southward of the parallel of Wicklow, and outside of the 
banks, there is, in the middle of the channel, a remarkable deposi- 
tion of shells. It extends at least as far as the parallel of Tuskar, 
where it is again succeeded by sand, which composes most part of the 
flat called the Nymph bank. 
This extensive shelly bed necessarily implies a peculiar supply of 
calcareous matter; and it is particularly remarkable, that the coun- 
try on either side cannot have produced it. There are no rivers of 
any consequence ; and the shores, on either side, are composed en- 
tirely of slate and granite. Here then is a substance composing 
the bottom of the sea, to a great extent, which is evidently not the 
result of alluvion. 
A similar extensive shelly bed occupies the centre of the wide 
part of the sea between Lancashire, Wales, and the Isle of Man, 
That portion of the sea however has limestone shores in Furness, 
Lancashire, Denbighshire, and Anglesea; and therefore the exist- 
ence of calcareous matter, in the bottom of the sea, may not be so 
remarkable. 
