524 Correspondence. 
which its thickness varies, is it not more probable that the same 
denudation which has produced in North Wales the numerous es- 
carpments of Lower Carboniferous rocks, has also cleared away the 
Millstone Grit and part of the Limestone at Pentre Celyn ? 
It did occur tome that the Pentre Celyn marls and shales might 
be some part of the Coal Measures; but, on the other hand, it 
appeared less likely that a break should occur (implied by the 
erosion of the Millstone Grit) between the Coal Measures and the 
Lower Carboniferous rocks, than between the Permian and the Car- 
boniferous series; and the close mineralogical resemblance of the 
strata at Pentre Celyn to the Permians in other localities seemed to 
warrant the conclusion expressed in my letter to the Magazine. 
Since it was published, I have again visited Pentre Celyn, and 
was fortunate in meeting with a number of plant impressions in the 
marly shales found in Mr. Edward’s pits. Mr. Etheridge has kindly 
examined them for me, and states ‘they are Permian or Lower 
New Red species, differing in all respects from Carboniferous.’ The 
fact is interesting, not only as affording evidence of a great erosion 
of the Carboniferous rocks before the deposition of the Permians, 
but as illustrating the possibility of the conformity of strata sepa- 
rated by an interval of denudation. 
Similar strata to those at Pentre Celyn intervene between the 
Bunter Sandstone and Carboniferous Limestone in several localities 
along the east side of the vale of Clwyd, as in the wood above 
Llandibr Farm (between Llandibr and Llangynhapal) and at Rhiw 
Bibbil, opposite Denbigh, &c. Is it possible that the beds Mr. 
Davies noticed crossing upon the western side of the vale, between 
the Limestone and the Sandstone in the cuttings of the Rhyl and 
Denbigh Railway, and supposed by him to be Coal measures, were 
Permian, similar to the strata on the east side of the vale of Clwyd ? 
—I remain, dear Sir, very truly yours, GrorcE Maw. 
BrenTHALL Hatt, Broserey, Oct. 7, 1865. 
GLACIAL STRILA# IN THE COUNTY OF LONGFORD. 
To the Editor of the GEOLOGICAL MAGAZINE. 
Sir,—In the last number of the GroLocicaL MaGaziIne there 
was an illustrated paper by Mr. A. H. Green, describing some sup- 
posed ice-scratches on a Limestone rock in Derbyshire. Mr. Green 
states that the Limestone is ‘studded with dark red patches of chert, 
which have been polished down to a smooth surface, and scored over 
with grooves and scratches.’ 
A similar instance occurs in Co. Longford, Ireland. On the 
northern slope of Slievegalry (a hill some five miles SSE. of Long- 
ford town, and 650 feet above the sea), there:is a considerable 
exposure of Conglomerate (Old Red), dipping N 30 W at about 8°. 
Tt consists of numerous pebbles and small boulders of quartz, and 
occasionally jasper, firmly cemented together in a base of coarse 
yellowish or reddish white sand. 
The pebbles have been worn and polished down to a flat surface, 
