26 _ NOYES ON THE GEOLOGY OF 
If the great ice-sheet was long stationary, it must have left a 
great morain, but we do not find any such thing, so we infer 
that when the ice began to recede it did go back steadily, and 
any small moraines which had been formed were washed away 
by the sea. 
Now we must examine the composition of the Drift of the 
Vale of Clwyd, which from its general character I would refer 
to this period, 7.e., the period of the encroachment of the sea 
immediately upon the recession of the glaciers. 
Which part belongs to the encroaching sea during the period 
of submergence, and which to the receding sea as the land came 
up again, I have not evidence strictly to define. The period of 
submergence, being essentially one of accumulation, should 
be marked by heavy deposits of clay as well as sand and 
gravel. Whereas the period of emergence, during which the 
shallow water conditions come into operation last, is more 
especially a time of destruction and winnowing out of the softer 
deposits brought within the action of the sea waves. The results 
we should expect to find in sand and shingle and broken shells. 
Though it would be difficult to map them out it is clear that 
there are two drifts in the Vale of Clwyd. The older consisting 
chiefly of clayey deposits, with none but rocks from the Welsh 
hills; the newer being a drift in which local débris bears a larger 
proportion to fragments from the Welsh mountains, and 
containing also a great variety of rocks which seem to have come 
by sea, viz., Scotch granite, Lake Country rocks and flint, with 
numbers of broken shells. 
The clays and sands in the Vale have generally a purple tinge 
derived from the New Red, which furnished a large part of the 
sand, or sometimes perhaps derived second-hand from the red- 
stained Carboniferous Rocks. This colour does not generally 
affect the gravel, and does not often extend much beyond the 
Vale itself. For instance, the gravel of Talargoch is grey, and, 
though a red sand occurs in the gorge of the Elwy fairly round 
the corner by Dolben, yet the clay and gravel drift immediately 
beyond by Dol, and on the hill-top by Bryn-y-pin, is not stained. 
In all this division of the drift flint occurs. The occurrence of 
flint, is, I should say, for this area the most characteristic feature 
of the deposit. It is not flint ice-borne from chalk, but rolled 
gravel-flint often with the ferruginous rusty gravel-stain re- 
maining. It looks as if it must have travelled on shore ice, 
or with some shore-travelling shingle, when the submergence 
allowed currents from the east to run through by Chester. 
To this stage I refer the Macclesfield beds and the Moel 
Tryfaen beds, and the greater part of Mr. SHone’s Cheshire 
Drift, all of which contain flint. Among the other included 
fragments we have of course samples of almost all the rocks 
of the Welsh mountains from which came the great ice that left 
the easterly striae, but we have also Criffel granite and St. John’s 
