THE VALE OF CLWYD. 25 
was carried to the ice-foot far away. But when the climate 
became milder, as the land went down the ice receded, leaving 
at successive stages glacial débris varying as time went on and 
the conditions changed. Still a large number of stones would 
be carried from the Welsh mountains, but a smaller proportion 
of these would be glaciated New peaks would continually 
stand out from the shrinking ice, and lines of boulders from 
them would be found. To this period we must refer the blue 
boulder-clay with felsites and other igneous and metamorphic 
rocks. Such as that in the Elwy valley, near Dol, or that at 
the bottom of the cutting made for the reservoir at Llanefydd 
(see fig. 12.) 
FiG./ 12. 
Section seen tn cutting made to procure clay for reservoir at Llanefydd. 
a. Peat, with timber a foot in diameter .............-.- 0005 
6. Gravel and sand, such as might belong to stream now 
running down the valley ; clay with rootlets ot Bhs 
c. False-bedded and irregularly curved beds of sand and 
gravel; very ferruginous in places; lines of clay 
(perhaps only older and deeper beds of 0.) ........ 10 
d. Very fine pale chocolate clay, sometimes laminated ; cut off 
very irregularly by lines and beds of black shiver and 
sand. This bed passes in places rapidly intoe. ...... I0' 
e. Blue clay, with fragments of stone, few of which are striated ; 
most of the rocks are of local origin .......... 10’ to 20! 
NEWER PLEISTOCENE. 
The sea soon followed the receding glaciers over the sinking 
land, and now our evidence becomes more clear. For though 
the temperature was still low, the sea was full of life, and 
shells were thrown up in the sand and shingle along the shore, 
and have been preserved in many places. Here we must bear in 
mind that the very existence of great masses of ice in the neigh- 
bourhood must reduce the temperature, so that if there were 
mountains high enough to have snow all the year round, or even 
glaciers, in North Wales now, although the other conditions 
which affect climate might remain the same, still it would be 
very much colder on the coast of North Wales than it is. 
Provide conditions that will bring glaciers down to within a few 
feet of the sea, then the existence of the glaciers themselves 
will cause such a reduction of temperature that they will get to 
the sea, and vice-versé. So when things began to go against the 
glaciers they probably receded fast, and the sea first rolled in over 
ground it might have covered before had not the ice advanced 
to meet it far off shore. To this state of things we must refer 
the mixed drift, which sometimes contains great masses of 
boulder-clay unsorted by water, and sometimes stratified sand 
and gravel, and this is properly the end of the Glacial Period. 
The sea worked away at the old glacial deposits along the hill 
sides, and in the Vale of Clwyd used up much of it to form the 
Clwydian Drift. 
