BEVAN ON THE SOUTH WALES COAL-FIELD. 



93 



Newbridge, in Glamorganshire, othei-Avise called Pontypridd, is 

 situated on the anticlinal axis, which has the effect of bringing up 

 the lower measures at Maesteg ii^on-works in the Llynvi valley. It 

 is marked by the appearance of a rock termed the " Cockshort 

 Rock," which consists of a bed, or beds, of sand, consolidated 

 together so as to form a quartz-rock : by miners it is known in 

 some districts as " carreg," or " craig gwenith faen" — the wheat- 

 grained stone, and is important as being the only wliite quartz-rock 

 in the field ; it is a serviceable guide to the relative position of 

 certain beds of coal. Its course is from Baglan, near Briton Ferry, 

 to Cwm Avon, Maesteg, Braich-y-cymmer, across the Llangeinor 

 Mountain," Cillely, and Newbridge, to the Eghvysilan Mountain. We 

 find the trough again, although wonderfiiUy narrowed at the 

 western end of the field, at LlaneUy, Caermarthenshire. The smaller 

 trough is directly south of the lai-ger one, and in fact occupies aU the 

 distance between the great anticlinal axis and the southern crop of 

 the basin. As a consequence, the beds of the south crop are much 

 more highly inclined than those on the north. They are also of 

 much greater thickness, showing a progressive tendency to thin-out 

 as they approach their northern Hmit. 



The faults of the South Wales field are numerous, and often locaUy 

 extensive, though there are none of general magnitude like the 

 Ninety Fathom Dyke. The largest faults are to be found in the 

 north-eastern part of Glamorganshire, running south-west from 

 Merthyr, across the Gellygaer-hill to Llancaiach, where it is one 

 hundred yards, so that the Mynyddswlyn-vein of coal, which is 

 worked by level at Tophill, is obhged to be worked by deep pit at the 

 Llancaiach Colliery, only a few hundred yards to the south. 

 Another great fault, runs westward from Trevethin, near Pontypool, 

 to Blackwood, where there is a perfect chaos of faults, the appearance 

 which on the Geological Survey's map reminds one strongly of 

 Bradshaw's Railway-map. The whole of the south crop is much in- 

 tersected by faults, particularly in the west of Glamorganshire and 

 Caermarthenshire ; but their small size prevents their having any 

 general interest. Nevertheless, it is highly important that even 

 small faults should be duly chronicled, for many instances might be 

 recorded where ignorance of existing disturbances has caused a 



