B. Smith — Glacial Gravels of Corwen. 315 



narrows northward in the direction of Gwyddelwern. It also 

 occurs on both flanks of the flood-plain in the valley east of Corwen. 

 This plain is probably floored by boulder-clay, because its surface 

 is diversified by low patches of undrained marshy ground where the 

 gravels are thin or absent, not through denudation, but apparently 

 because they have never been deposited there. From our own 

 observations this boulder-clay, on the hill-slopes near Corwen and in 

 the Dee valley farther east, comes out from beneath the gravels and 

 river deposits and ascends to higher levels. 



Corwen Gravels {Details). — We may take it that Mackintosh's 

 description of the succession of the deposits is, as usual, correct. The 

 sands and gravels and the occasional irregular kind of brick-clay 

 over-lie boulder-clay with beds of coarse gravel. The cuttings along 

 the railway north of Corwen, examined by Mackintosh, are now, 

 unfortunately, grassed over to a great extent ; but it is still clear that 

 an irregular deposit of layers and lenticles of unevenly-bedded gravels 

 and false-bedded sands and silts on silty loam (? brick-clay) is over- 

 lying boulder-clay which appears here and there at about rail level. 

 The beds dip almost due east. A section on the left bank of the 

 Nant Fawr, south of the line, contained masses of gravelly clay, 

 loam, and clayey gravel like boulder-clay with intercalated sands. 



About half a mile N.N.E. of Corwen, at the junction of the Carrog 

 road, north of the river, with the by-road to Tan-y-gaer at the east 

 end of the bridge over the railway, 2 feet of soil with boulders rests 

 on 2 feet or more of partly stratified loam with stones, on 3 feet of 

 pebbly gravel. The loam is generally grey or grey-brown, but 

 contained small patches of brick-red sand, rusty or yellowish-red sand, 

 and streaks of bluish clay. The stones were partly rounded, partly 

 subangular. Many were of igneous rocks, but none were of types 

 that might have come from the Irish Sea area. There were also 

 occasional cherts and sandstones. 



Similar deposits extend as far north as the railway cutting south 

 of Gwyddelwern, where, at about 580 feet O.D., they die out above 

 the boulder-clay. 1 



Turning again to the Dee valley we note that in a pit in the gravel 

 terrace near Groes-faen, about 530 yards west of Carrog Church, the 

 beds were unlike ordinary river gravels. The dip is in all directions, 

 and the deposit is silty, sandy, and gravelly in streaks and patches, 

 often inclined at high angles. Some patches are clayey, others of 

 fine loam with a feel like French Chalk or Fuller's Earth. 



The following section was exposed at one point in the south side 

 of the pit : — 



ft. in. 

 Coarse gravel and pebbles . . . about 2 



Grey silt and sand .... ,, 6 



Pale fine gravel ..... ,, 6 



Light-brown finely laminated clay . , , 10 



1 In a north-easterly direction towards Bryn Eglwys the boulder-clay is 

 associated with very little sand or gravel, but makes good drumlin scenery. 

 The exceptions are some morainic sands and gravels in the valley at Bryn 

 Eglwys and near the southward bend of the Afon Morwynion, north of the 

 Carrog Gap. 



