8 DEPOSITION OF SEDIMENT IN THE DEE, 
other species of Bivalve-shells, which do not occur nearer the 
shore. Further out still are beds of pure sand, which the natives 
call ‘“chaffy banks,” from their dry and chaff-like character. 
I believe these to be almost, if not quite, devoid of animal life. 
‘On the other side of the river, in Dawpool, where the water is 
deeper, you get mud again, but now inhabited by great 
quantities of mussels, which do not occur at all on the Welsh 
side. Thus you will see how great a variety of totally dissimilar 
deposits are going on simultaneously in a small area, and for 
the most part between high and low water mark of the most 
ordinary tides. I cannot but think that the only chance of 
unrayelling the tangled skein of difficulty that surrounds the 
phenomena of the boulder clay, lies in a careful examination of 
such deposits as are going on at the present day, and I would 
strongly recommend the estuary of the Dee as a promising field 
for such investigation. 
The sand deposited by the river reaches (in places, at all 
~ events) to a great depth. Mr, Jonson who superintended the 
sinking of the shaft of the Bettisfield Colliery at Bagillt, informs 
me that they sank through 50 to 60 feet of river sand before 
reaching the clay. On the surface of this clay they found large 
boulders partially embedded in it. The under-side of the 
boulders was more or less angular, while the upper surface was 
rounded as if by the action of the waves, or perhaps of fine 
gravel and sand continually driven over it by the current. 
Attached to the stones were oyster shells showing that the 
stones had not been shifted from the position they occupied 
when the oysters upon them were living. At that time, if there 
had been no subsidence since, the water immediately under the 
high bank which runs all along the river must have been 50 or 
60 feet deep; but as I believe this is a greater depth than oysters 
usually inhabit, and bearing in mind the submerged forests at 
Leasowe on the one side, and Llandrillo on the other, we are 
justified in concluding that though the actual bed of the river 
has been raised by silting up, yet there has been a general 
subsidence of the whole coast. 
