THE GEOLOGIST. 



63 



1 append a section of the grit, or, as it is locally termed, Farewell 

 Hock, 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 Irongton© 



containing shells. 

 Strong grey sandstone. 

 Dark do. and argillaceous shale. 

 Dark grey sandstone. 

 Argillaceous shale. 

 Dark grey sandstone. 

 Light brown do. 



ConglomeratCj or plum-pudding stone. 



Brynmawr is a large mining town, with a poptilation 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 present small 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. 



