4 
DE RANGE : 
THE VALE OF CLWYD CAVES. 
The Glacial Drift of the north-west of England and the coast of 
North "Wales is generally made up of an Upper Boulder Clay, 
reddish or brown in colour, traversed by vertical joints, in the neigh- 
bourhood of which the colour of the clay is generally of a leaden hue, 
it is obscurely stratified, contains rounded and semi-rounded pebbles 
and blocks, that had been previously ice-worn and scratched, probably 
by the action of coast-ice, shells of recent mollusca occur occasionally, 
but generally in a fragmentary condition, and have probably been 
derived from the gravel generally found beneath these gTavels, or 
rather shingle beds associated with thick beds of sand, have been 
called the "Middle Drift," from their overlying a Lower Boulder Clay, 
where seen in section, as in the Bispham and Norbreck Cliffs, north 
of Blackpool, the banks of the Kibble Valley at Red Scar, east of 
Preston, the cliffs near Egremont, in Cheshire, and Mostyn, in Flint- 
shire. The pebbles in the Middle Drift are invariably derived from 
the underlying or immediately adjacent local deposit, and are made 
up of fragments of coal, coal measure sandstones, or millstone grits, 
if these rocks underlie it, or of erratic pebbles derived from the 
Lake District, if the Lower Boulder Clay forms the underlying deposit. 
The sands are extensively current-bedded, generally in a S.S.E. 
direction, or that now taken by the tidal current flowing past the 
Mull of Cantyre, on the coast of Cumberland, and that of Morecambe 
Bay, where this portion of the tidal current now meets that flowing 
through St. George's Channel, which during the glacial submergence 
was not the case. Shells of recent mollusca occur plentifully in pebbly 
seams, the shells aregenerally fragmentary, but at Macclesfield, Leyland, 
Preston and Blackpool they occur in a perfect condition, and probably 
lived at the site of the localities, where they are found, when covered 
by the glacial sea, the species of many are northern, and resemble 
those now living at the North Cape ; in the peculiar thickening of the 
canal of the univalves, and the umbos of the bivalves, they resemble the 
shells of recent mollusca, brought back from Grinnel Land, by the late 
British Arctic Expedition. A similar assemblage of shells is found in 
the sands, occuring at very different levels, varying from that of the 
present high- water mark to 1,200 feet above it, it is probable that the 
deposits of the higher elevations are more modern than those of the 
