THE GEOLOGIST. 
53 
1 append a section of the grit, or, as it is locally termed, Farewell 
Eock, an expressive name given by the collier, although, as will be 
seen, it is not quite destitute of coal seams occasionally : — 
Section of 80 yards. 
Sandstone. 
Strong white sandstone. 
Sandstone and argillaceous shale. 
Sandstone. 
Argillaceous shale. 
Coal, four inches. 
Sandstones and shale beds. 
Coal, one foot six inches. 
Blue Sandstone. 
Brown do. 
* Argillaceous shale, with small pins of Ironstone 
containing shells. 
Strong grey sandstone. 
Dark do. and argillaceous shale. 
Dark grey sandstone. 
Argillaceous shale. 
Dark grey sandstone. 
Light brown do. 
Conglomerate, or plum-pudding stone. 
Brynmawr is a large mining town, with a population of about 
8,000, which has sprung up as a feeder to the important 
works of Nantyglo and Beaufort. It is placed very near the 
outcrop of the coal measures, and at the head of one of 
the parallel vallies which I mentioned before. The guardian 
hills on each side are composed of Pennant grit or sandstone, which is 
usually considered as a middle series, separating the upper from the 
lower coal measures. These rocks attain a great thickness, and are 
characterised by a thin roofing sandstone, in form and appearance 
very like the hollybush sandstone at Malvern, but covered with minute 
carbonaceous specks. The beds are stratified very regularly, with but a 
slight dip, and presentsmall and confused traces of vegetation. According 
to Sir Henry dc la Beche they were found in the following manner : — He 
considers the principal mass of sand to have been forced along the 
bottom by the pressure and movement of super-incumbent water, but 
° To this layer I shall afterwards more particularly allude. 
