Vol. 58. | THE RIVER-SYSTEM OF SOUTH WALES. 211 
effects are well exhibited. Here again is a no less intimate connection 
between disturbance and river. The Tawe is fed by streams from 
the Old Red Sandstone. These unite before reaching the Carbon- 
iferous Limestone escarpment, and pass that great feature in a 
winding gorge, near, but not along, the line of the Cribarth dis- 
turbance. In the Coal-Measures, however, a little to the south, 
the river falls into the line and follows it thence to Swansea, a 
distance of about 12 miles. ‘The disturbed belt is less closely 
defined than that of the Vale of Neath; but evidence of its 
existence recurs at frequent intervals. The Red Vein of coal, for 
example, is thrown down to the north-west at Ystalyfera, and the 
Hughes Vein is similarly shifted near Pontardawe. Some great 
north-and-south faults are deflected by it in a manner described 
later on; while, lastly, in following the line of disturbance to 
Morriston near Swansea, we are led to an extremely deep faulted 
syncline, known as the Tir Canol Fault, which has been thoroughly 
explored in working the coals under the alluvial flat. There is no 
known fault, however, in the gorge by which the Tawe traverses the 
southern escarpment of the Pennant Grit at Swansea. 
The Loughor River rises in the northern margin of the Car- 
boniferous area, and runs in a direction slightly west of south. 
It follows no great line of disturbance, but meanders across the 
Coalfield, passing several considerable north-north-westerly faults 
and east-and-west folds without deflection. 
The Towy flows wholly on the north side of the Carboniferous 
area. It is fed by a number of streams from the main water- 
parting which runs through the counties of Pembroke, Cardigan, 
and Montgomery; but these tributaries are all gathered into a main 
stream, the course of which from Llandovery by Llandilo to Car- 
marthen is obviously connected with the strike of the Silurian and 
Ordovician rocks. Recent work by my colleagues Messrs. Cantrill 
and Thomas’ has shown that that strike is due to movements of 
great energy, which have not only rendered the strata vertical, or 
nearly so, along a belt of country some 2 miles in width, but have 
caused much overthrusting. The disturbance (A onthe map, Pl. V), 
which may be conveniently named after Llandilo, is allied in 
direction and character with those of Cribarth and Neath, as will 
be shown in discussing the age of the various movements evidenced 
in South Wales. Near Carmarthen, where it loses energy, it 
releases the river, which then takes a southward direction into 
Carmarthen Bay. JBefore quitting the Towy, however, brief 
allusion may be made to a small tributary known as the Cennen, 
which rises in a Strike-valley at the foot of the Carboniferous- 
Limestone escarpment. The valley follows a subsidiary disturbance 
' (B onthe map, Pl. V) parallel to the Llandilo movement, the effect of 
which has been to form a faulted syncline, and to introduce a con- 
spicuous little crag of limestone, known as Cerig Cennen, into the 
middle of the outcrop of the Old Red Sandstone. The drainage 
1 Mem. Geol. Surv. Summary of Progress for 1901. (In the press.) 
G7 3.6. 8, No..230. ) 
