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PROF. T. M'KENNY HUGHES ON THE 



It is about 50 feet from this to the bottom of the valley, but the 

 whole section, though changing from year to year, is generally much 

 obscured by slips and talus, especially towards the base, so that I 

 could not make out whether there was rock at the bottom of the 

 section here. It does occur at this level on the other side of the 

 valley. 



These sections show that we have a variable deposit of gravel 

 and sand and boulder-clay ; and we must now examine in greater 

 detail the constituents and general characters of the beds before we 

 carry our identification further. There seems to be occasionally a 

 surface -gravel, coarse and grey, the result of the winnowing of the 

 St. Asaph Drift during the emergence ; but the highest beds, espe- 

 cially along the central part of the valley, generally consist of red 

 boulder-clay, the middle of sands and gravel, with subordinate clay 

 and loam, the bottom of re-sorted boulder-clay or sand resting on the 

 old blue boulder- clay, some of which, at any rate, seems to belong 

 to the more ancient western land-ice drift. 



Again we notice two distinct groups of included fragments — one 

 consisting entirely of those with which we have become familiar in 

 the Arenig or ice-drift. These are stones from the far-off mountains 

 of Wales, and others which the ice carried from much nearer to 

 where they now lie. Where they have been dropped into clay the 

 scratched stones retain their striae ; where they occur in gravel the 

 scratched stones are rare, and only " the ghosts of scratches " can 

 be seen. 



But there is another group of rocks, none of which are scratched. 

 Among these there are many which do not occur in place in Wales 

 at all. They are in form and surface like the stones found on any 

 beach. 



The characteristic rocks are Scotch and Lake-district granite and 

 other igneous rocks and flints. This is true chalk-flint, not chert 

 from Carboniferous rocks, of which there is also some, though rare ; 

 for the principal chert-bearing strata had by this time been removed 

 from the country west of the Yale of Clwyd. These all occur both 

 in the gravels and the upper clays. 



In the south part of the section, near Brynelwy, I have found an 

 angular fragment of one of the scratched boulders buried in the clay. 

 This boulder had probably been exposed in some preexisting cliff of 

 boulder-clay, had been shattered by frost or sun or fall, and one bit 

 had dropped unrolled into the depth below, where it was buried in 

 the mud and preserved from further injury. Thus it retained the 

 sharp fractured edges, and also one face, which had formed part of the 

 surface of the ice-scratched block. This, I take it, was a stone out 

 of a cliff of the old Arenig ice-drift, which was washed by the sea 

 in the submergence during which the St. Asaph Drift was formed. 



I have found also in the sand and gravel of the same section 

 clay-balls, containing inside only fragments of Welsh rocks, but 

 with pebbles of the gravel stuck all over the outside, just as I have 

 se en balls of alluvial clay or older boulder-clays rolled on the shore 

 near Prestatyn, or Pensarn, or Colwyn, or near Penrhos in Anglesey, 



