DEPOSITION OF SEDIMENT IN THE DEE. 7 
process can be proved by the fact (for which I am indebted to 
my friend Mr, Dick, a most careful and accurate observer) that 
it may be seen in action at this day whenever there occurs a frost 
severe enough to form masses of ice on the Dee. For after 
such a frost, the mud banks off Flint and Bagillt may be seen 
thickly sprinkled with stones, the masses of ice that have 
brought them haying melted, but in a short time all these 
stones have vanished. They must have either sunk into or 
been covered up by the mnd. But the latter hypothesis is 
hardly tenable, as it involves a rise in the height of the banks 
much more rapid than actually occurs, so that we are driven 
to the conclusion that they must have sunk into the mud, 
though it is a question how far they would sink. This might 
explain, in many cases, the occurrence of the pebbles thinly 
scattered through the brick-clay, for had they been deposited 
at the same time as the clay, they would have been arranged 
more regularly in layers or strata according to their size, &c. 
The bed of the Dee offers a good example of the danger of 
inferring, from the difference in character of deposits, that they 
were not of the same age. If anybody will walk across the 
Dee from Bagillt to Parkgate he will find that he passes over 
some strikingly different deposits, all of which, however, are 
going on simultaneously, and side by side. First in order, he 
will come toa greasy, slippery mud, so riddled by the burrows 
of a small Crustacean (Corophium longicorne), and a Nereid 
worm, that, of the former especially, every square foot of mud 
contains many hundreds. When this mud is dug into it is 
blackish in colour, and has an offensive smell; and at a lower 
depth than the animals above-named, are found many specimens 
of a large shell-fish, Mya truncata. It has always struck me 
that this mud would, in the course of time, acquire much the 
same appearance as the flag-stones we saw last summer in the 
Quarry at Greenfield, and which belong to the lower Coal 
Measures. Well, continuing our walk, we should reach, about 
a mile from the shore, large banks of wet sand, which are 
the chosen home of Cockles, Lug-worms, and two or three 
