682 MR. T. aCELLAILD READE 0^' HIGH-LEVEL [Aug. 1 898, 



38. High-Level Mapjxe Detfi at Colwtx Bat. By T. Mellard 

 Eeade, Esq., C.E., F.G.S. (Eead June 22iid, 1898.) 



[Abstract.] 



The drift' deposits of Colwyn Bay were described by the Autlior in 

 18S5/ but at that time he did not find any marine drift above the 

 200-feet contour. In the vrinter of 1897-98 he was fortunate 

 enough to discover a mound of marine drift, consisting of sand 

 capped with Boulder Clay, at a level of 560 feet above Ordnance 

 datum. It is situated at a distance of about 1 mile south-bv-west 

 of Colwyn Bay railway-station, the longer axis running in a north- 

 easterly direction, and measuring about 90 yards, the shorter axis 

 being about 50 yards in length. It stands upon the watershed sepa- 

 rating the valleys of Xant-y-glyn and Colwyn Bay. It is evidently 

 an outlier of the marine drift; at a lower level, consisting as it does of 

 the same well-rounded grains of quartzose sand, and containing far- 

 travelled erratics, among which are Eskdale and South of Scotland 

 granites mixed with TTelsh rocks, many of which, according to 

 Mr. T. Euddy, to whom they were submitted, came from the head 

 of the Conway Valley. The interest of this find lies in the appa- 

 rent isolation of the mound and its situation on the watershed at a 

 high level. The intervening ground between the mound and the 

 marine drift skirting the coast is occupied with blue Till, the pro- 

 duct of lc:nd-ice, in which only "Welsh rocks are found. High-level 

 marine sjuds are found flanking the Vale of Clwyd on the Flintshire 

 side, but the Author knows of no record of high-level marine drift 

 in the neighbourhood of Colwyn Bay. There is no doubt that the 

 formation of the mound is geologicallv subsequent to that of the 

 blue Till. 



The Author further describes stratified marine sands containing 

 shell-fragments, resting upon brown Boulder Clay, exposed in three 

 sandpits near the Old Colwyn Eoad at Groes, on the east side of 

 ;jyant-y-glyn. At Old Colwyn. on the east side of the valley, there 

 is a great development of a similar sand lying bet\^ een the 100- and 

 200-feet contours, also containing shell-fragments. A depth of 

 30 feet of this sand was exj osed untottomed, and it is probably as 

 much as 60 feet deep. On the west side of the valley, below the 

 lOO-feet contour, an excavation for a house showed angular and 

 subangular gravels of Welsh rocks containing a lenticular seam of 

 sand with rounded grains, and this appeared to be a passage between 

 tbe purely land-ice or fluvial drift and the geologically overlying 

 marine sands. It is a notable fact that the marine sands of Groes, 

 of Old Colwyn, and of the Vale of Clwyd lie on the east side of 

 their respective valleys, while the marine Boulder Clays lie to the 

 greater extt-nt on the west side ; and that the marine sands have 

 mostly accumulated as bars near the mouths of the valleys. 



^ Quart. Joum. Greol. Soc. vol. xli, pp. 102-107. 



