452 D. MACKINTOSH ON BEDS OF DRIFTED 



Derivation of the Drifted Coal. — In order to arrive at a satisfactory 

 conclusion on this subject, it may be necessary to take into account 

 the direction of the glaciation in the neighbourhood of Corwen. 

 On the north slope of the hill to the south of the town, after care- 

 fully eliminating a number of structural furrows on rock- surfaces, 

 which could be traced to where they ran under overlying strata, I 

 found true glacial striae coinciding with the rounded sides of rocky 

 projections pointing to about W.S.W., or approximately in the 

 direction from which the boulders of the district were transported. 

 This at first led me to suppose that the coal had been drifted from 

 W.S.W.; but this involved the supposition that a portion of the coal 

 formation in situ must have been faulted down * on the top of the 

 remarkable outlier of Mountain Limestone which occurs about a mile 

 and a half west of Corwen, and that, as the limestone strata dip 

 between E.N.E. and N.E. at an angle of about 45°, the coal in situ 

 must have remained in a depression (now covered with drift) on the 

 east or dip side of the limestone until the glacial period, if not 

 until the present time. After corresponding with Mr. Aveline (who 

 formerly surveyed this part of Wales, and who informed me that he 

 regarded the above theory as very improbable), and after reconsidering 

 the subject, I became convinced that the drifted coal around Corwen 

 must have come from the Cefn and Euabon district, about 12 miles 

 east of Corwen in a straight line, but at least 20 miles following the 

 sinuosities of the valley of the Dee. The height above the sea of 

 the drifted coal in the cutting north of Corwen is about 550 feet, 

 which is not high enough to preclude the idea of its having found its 

 way from the above district ; and this idea is corroborated by the 

 similarity of the Corwen to the Euabon coal f. 



Mode of Transportation of the Corwen Coal. — As no boulders, 

 striated stones, or other traces of glacial action are to be found 

 immediately associated with the drifted coal under consideration, it 

 would seem that it must have been transported during a compara- 

 tively temperate interglacial period when very little ice floated on 

 the surface of the sea, but still sufficient ice to carry lumps of coal 

 (though not large fragments of rock) as far as Corwen. The limi- 

 tation of the Corwen coal to a low level suggests the idea that at 

 the time of its transportation the land was not submerged beyond 

 a few hundred feet, and that the coal was floated along the sinuosi- 

 ties of the valley of the Dee, until, arriving at shallow water in the 

 Corwen area, it stranded, and became imbedded in sand by sea- 

 currents or waves. It is not necessary to suppose that there was 

 any thing more than a tidal current flowing up the Dee valley at the 

 time when the coal was floated. 



Principal Bearing of the subject on Glacial Geology. — If the fore- 

 going be a correct explanation of the derivation of the Corwen coal, 

 it follows that during the glacial (including interglacial) period, the 



* The great Bala fault, which divides the whole of North Wales into two 

 parts, runs through the Vale of Corwen. 



t In the drift around Ruabon and Wrexham there is a considerable quantity 

 of coal debris, showing that at least a local drifting of coal must hare occurred. 



