268 Prof. J. F. Blake—Shell-beds of Moel Tryfaen. 
been submerged, not locally, so as to reduce the relative level of 
these moraines, but over the whole of Wales. 
But now comes the real difficulty. The shell drift is on the other 
side of Moel Tryfaen and the moraines have no direct connection 
with it. The uppermost and best defined of these stretches in a 
continuous mound from Braich Melyn Smythaw by Moel Tryfaen 
village to the slate railway incline. To the H.SH. of this is the 
high ground of Moel Tryfaen and Moel Smythaw, both of which, 
on their western slopes, on their summits, and on part of their 
eastern slopes, are entirely free from drift; and there is only about 
a quarter of a mile between exposures of live rock on either side of 
the pass between the two through which the drift could be carried, 
and this path is at right angles to the trend of the moraine. It is 
difficult. to say whether these hills have ever been glaciated. The 
temptation to think so is afforded by the great projecting masses of 
conglomerate which so characteristically cap the summit of Moel 
Tryfaen, the rest of the hill being of a more generally rounded 
form. This is so like what we may imagine to be the phenomenon 
of a nunatak that it is hard to resist the idea of its being such. 
Still we may easily account for it otherwise; for the hardness of 
the conglomerate resting on softer rocks would be an adequate 
cause, as in the case of the Brimham rocks of Yorkshire. I am 
not aware that glacial striae have ever been found on the upper 
parts of these hills. There are numerous unrounded crags about on 
the surface, and the rocks on Moel Tryfaen—where there is a good 
variety—lie on the surface so accurately in order (now that that 
order is known) that they must have weathered in sifu and not 
have been moved since. So that if ever the ice were there it must 
have been so long ago that all signs of it have been obliterated and 
the signs of ordinary weathering have taken their place. 
These two hills form part of a long boundary which separates 
two very distinet glacial areas. Moel-y-Ci, Rhiwwen, Clegyr, Cefn 
Dui, Moel Smythaw, Moel Tryfaen and Mynydd-Cilgwyn, from a 
range, on the west of which we find moraine-like heaps with foreign 
boulders, while on the east the boulders (as far as I have been able 
to discover, and with the exception of Moel Tryfaen deposits) are 
not of foreign origin, and the drift is not spread out in the form of 
moraines. I take it that these hills stood like outposts to the 
North Wales camp in glacial times and forbad the invader to over- 
step their lines. 
The nature of the problem to be solved must now become evident. 
How is it that these shelly deposits have found their way within the 
North Wales line? Why do we find within this area a deposit 
which, though not of a moraine-like form, does contain foreign 
material including shells? And how is it that such deposits are at 
over 200 feet higher level than the highest of the moraines? For 
the solution we naturally look to the details of the deposits. These 
are at present beautifully shewn in the Alexandra quarries, which 
are being enlarged and the bearing cleared. From 30-40 feet of 
Glacial beds are exposed, lying on the irregular surface of the slates, 
