96 
THE GEOLOGIST. 
uppov-measuro seam east of tlio Taff. The Mynyddswlyn-vein, three 
feet thick, is the great vein from which the red ash, or home-burning 
coal is sent to Newport and CardiiF. It occupies a rather narrow 
tract of country, runing east and west from Pontypool to the Taff. 
The railway which goes across Cwmlin Bridge takes us through the 
very centre of this tract, which is very thickly studded with coUeries, 
and cut up with a number of small faults A good idea of it will be 
gained from the horizontal section of the Government Survey, No. 
12, as it runs through the Cefn Crib mountain to crop out at Cred 
Colynos, above Pontypool. It usually consists of a top- and bottom- 
coal, divided by a varying amount of rubbish, or parting — for instance, 
at the south-east crop of this vein, which is to be found at the 
Penner coUiery, near Newbridge, the division is thirty-three feet 
thick ; but on the north crop, at TophUl, near Llancaiach, overlook- 
ing the Taff Vale, it is only a foot and a-half ; so that the two veins 
can be conveniently worked together. I append a section of this 
coal as worked at the Mamhole-coUiery, in the Sirhowy Valley, the 
property of Sir. Thos. Phillips : — ■ 
Ft. in. 
Surface 19 6 
Rock 33 0 
Clod 8 0 
Thin coal (The Rider) 1 2 
Clod 30 0 
Rock 54 0 
Clod 30 0 
Coal (top) 3 0"^ 
Clod 1 6 > Mynyddswlyn 
Coal (bottom) 2 6) 
The clod soon begins to thicken, even in the space of a few 
hundred yards, as does the coal itself. 
From the measures at Pontypool several coal-plants have been ob- 
tained ; but the most interesting fossil there is found in the iron- 
stone, just above the Meadow-vein. It is the Produdus scabriculm, 
the only Productus ever found in the true coal-measures, and as far 
as I have been able to ascertain, the only specimens as yet found 
in the district. Here they are very plcntifol. 
As we follow np the Afon and Frwd valleys we successively arrive 
