B. Smith — Glacial Gravels of Corwen. 317 



Source of Coal in the Gravels. — The occurrence of coal debris in 

 the gravel varying in size from large lumps to fine dust, is a point 

 of great interest. Mackintosh records it (i) in a roadside section 

 immediately east of the Carboniferous Limestone Quarry (Hafod-y- 

 calch) about a mile and a half west of Corwen; (ii) in a railway- 

 cutting some distance east of Corwen and not far from Carrog 

 Station ; (iii) north of Corwen, near to where the Ruthin railway 

 crosses the River Dee — this was the principal locality. He was 

 also assured that coal could be found at many other places around 

 Corwen. 



After diligent search the author failed to find any coal, probably 

 because of the overgrown state of the cuttings, but residents in the 

 neighbourhood stated that coal had been found in the gravels. 



Mackintosh rejected the hypothesis that there might ,be 

 a concealed outcrop of coal-bearing beds in the neighbourhood, 

 and suggested that the coal was drifted some twenty miles up the 

 winding Dee valley from the neighbourhood of Cefn or Euabon, 

 during an interglacial submergence. This idea of submergence 

 cannot be maintained. 



The coal might have been derived from three possible sources : 

 (1) from the Vale of Clwyd ; (2) from the Euabon district; (3) 

 from a local outcrop. 



1. This direction of transport may be dismissed forthwith. South 

 of St. Asaph the movement of ice was from S.W. to N.E., and all 

 waters due to melting ice flowed northward. 



2. Any movement of coal from Ruabon must have been against 

 the general direction of glaciation, and must have been caused by 

 ice-bergs or water moving up the Dee valley, and escaping in 

 a south-westerly direction, owing to a huge ice-dam (Irish Sea Ice) 

 across the Dee valley below Llangollen. There is no evidence for 

 this as far as I am aware, nor has it been suggested by my late 

 colleague, Mr. L. J. Wills. The boulders in the Corwen gravels 

 include no rocks from the Irish Sea basin. 



3. Thus we are thrown back upon the theory rejected by 

 Mackintosh, namely, that the " very-little-waterworn " fragments of 

 coal could only have come from some now-buried or completely 

 destroyed outcrop in the vicinity. 



If we imagine that the Carboniferous Limestone at Hafod-y- 

 calch near Corwen was formerly succeeded by " Millstone Grit " 

 (Cefn-y-fedw Sandstone) and a considerable thickness of normal 

 Coal-measures, it may be difficult to believe that there is a local 

 outlier of the latter that has escaped detection north of the Bala 

 Fault; but when we remember that in the Vale of Clwyd the 

 so-called Millstone Grit is wanting and the Coal-measures are 

 represented by thin purple shales and sandstones 2 with occasional 

 thin coal-seams (one of which had shafts sunk along it) resting upon 

 the highest beds of the Carboniferous Limestone, belief in the 

 occurrence of Coal-measures near Corwen, which is only slightly 

 farther west, is strengthened. In the quarries at Hafod-y-calch 



1 The Geology of the Neighbourhood of Flint, Mold, and Ruthin (Mem. 

 Geol. Surv.), 1890, pp. 10-16. 



