Correspondence. 381 
stone, dipping about 42° to the S.W., and resting with an apparent 
conformity on the denuded surface of the Mountain-limestone, which 
in this part of the vale has a similar dip. These beds were pro- 
bably not visible at the time of the Survey, but are now exposed in 
quarries to the east and west of the road, and have recently been 
pierced by some pits sunk in search of hematite on its western or 
lower side. ‘They are very distinct in mineral character from both 
the neighbouring Millstone-grit and the Bunter Sandstone of the 
vale, and are an exact counterpart of the Permian series of Shrop- 
shire. 
- The Bunter Sandstone is well exposed a mile to the north-west 
at Garth Gynan, where it dips north-west about 25°, and would 
appear to be unconformable to the beds at Pentre Celyn, but the 
junction is not visible. 
Although the supposed Permian strata appear to rest conformably 
to the Mountain-limestone, the extreme thinness of the Limestone at 
this point, and the absence of the Millstone-grit, which is so largely 
developed close at hand, would indicate a great erosion of the 
Lower Carboniferous series before the deposition of the Permian. 
The Permian strata were here certainly deposited on nearly level 
Carboniferous Limestone; and if this were its original plane of de- 
position, the elevation, and probably the great dislocation, must have 
taken place between the Permian and the New Red period ; also a 
second great erosion before the deposition of the New Red Sand- 
stone. The Mountain-limestone, with its overlying Permian, must 
have been pitched up some 15° or 17° before the Bunter Sandstone 
was deposited against them, and then the whole further elevated to 
the extent of the present dip of the Bunter. 
That a great denudation of the Lower Carboniferous series took 
place before the close of the Permian, is also evident from the large 
number of fragments of Mountain-limestone that occur in parts of 
the Permian breccia round the Abbersley Hills, and on the banks of 
the Avon, near Bristol. 
From some facts I have recently observed i in Flintshire and Den- 
bighshire, I think the contour of the Mountain-limestone range of 
North Wales was not materially changed during the Glacial period : 
but that some further erosion did take place, is manifest from the 
abundant fragments of Mountain-limestone that occur in the Boulder- 
clay of the North Welsh coast. Ice-transported blocks of Mountain- 
limestone, weighing many hundredweights, and Mountain-limestone 
fossils also, fre equently occur in the Drifts and Boulder-clay of the 
Severn Valley. —I am, &c. GrEoRGE Maw. 
To the Editor of the GroLocicaAL MAGAZINE. 
Srr,— Your Correspondent whose observations appear on page 
236 of your Magazine for May falls into a serious error in sup- 
posing that the stratified and unfossiliferous clay, which appears 
upon the surface of the Lower Boulder-clay, at Heaton Mersey, near 
Manchester, belongs to the Upper Boulder-clay division. Yesterday 
I paid a visit to the locality, and, after comparing his notes with 
the sections that are now to be seen, it is evident that they are not 
