142 Mr Buchanan's Report on the Bridge (xf Suspension 
solate and sandy marsh. (See PL VII.) But what we have chiefiy 
to consider here, is the difficulty of finding in such a situation any 
solid foundation for the erection of a bridge. In consequence of 
the violence with which the water flows out and in, as the basin 
is alternately emptied and filled, the natural channel of the river 
has been deepened, and now contains in the middle parts a body 
of 30 or 35 feet of water at full tide, and never less than 9.0 feet 
at the lowest tides. The current also often runs at the rate of 
five or six miles an hour. The river Thames at London is 
broader than this stream, but its depth is much less, and its cur- 
rent is not nearly so rapid. Estimating the average depth of 
the basin to be six feet at high water, and its area four square 
miles, we shall find that the body of water discharged through 
this channel, is equal to that of a river which drains a country 
10,000 square miles in superficial extent, a surface far exceed- 
ing that which is drained by the principal rivers of our island, 
and more than double the area drained by the Thames itself. 
It is not therefore merely a fresh-water stream over which we 
have to build, nor yet, strictly speaking, an arm of the sea. It 
is a vast river from the ocean, pouring in with rapid stream on 
our works, and in a channel already of uncommon depth, and 
at the same time so confined, and of so soft and yielding a bot- 
tom, that the least contraction of the water-way is sure to deepen 
it still farther, and thus endanger any work erected on so pre- 
carious a foundation, should the attempt even succeed of found- 
ing and building, in a situation so replete with difficulty and 
hazard. 
At the place where the bridge is erected, the river is divided by 
a small island called the Inch into two streams, which again unite 
at a quarter of a mile below the bridge. It is over the northern 
and larger stream that the bridge is erected, the dimensions of 
which have been already stated generally, and will be found more 
minutely laid down in the annexed engraving, PL VI. The south- 
ern channel is much smaller than the northern, being scarcely 
half its size, and is crossed by a stone-bridge consisting of only 
one arch, but so narrow, that it has contracted the channel of the 
river, to at least one-fourth of its original breadth. The conse- 
quence of this is, that the greater part of the stream which for- 
merly ran through this channel has been diverted into the north- 
