76 pkoceedings of the geological society. 



Tkansyerse Section oe E-hondda Valley. 



The Rhondda river unites with the Taff river twelve miles below 

 Quaker's Yard, and fifteen miles from its source. 



The transverse section across C measures 1730 yards from the 

 opening of the levels on the opposite sides, 84 yards on the west side, 

 and 79 yards on the east side, above the level of the E-hondda river, 

 at the point C. 



The gradient from the west level (D) to the river is 1 in 13, 

 that from the east level (C) is stiU steeper, being 1 in 8 J ; so that 

 the sides of the valley slope at 1 in 11 on the average (from C and 

 D to the river), or at an angle of 8°. The point C is about four 

 miles from the furthest watershed of the river beyond. 



Below the level of the quarry, on the west side, above the river, 

 there is no rock seen except at one point in a watercourse. 



The dip of the Coal-measures at this point (D E) is about 3° north, 

 and the section (PI. IV. fig. 3, DE) is nearly east and west. 



The escarpment of the high ground above T> and E is nearly twice 

 as steep and high as that of the South Downs, and pursues its course 

 nearly north and south along each side of the E-hondda valley. The 

 dip varies, sometimes being northerly, and at other times south. 

 This is marked by the arrows in the Ordnance map ; and the lines of 

 outcrop of the coal also show the direction of the escarpment. The 

 escarpment, therefore, in the E-hondda valley is in the direction 

 of the dip, and not of the strike ; and the dip changes without any 

 alteration in the direction of the escarpment. In fact, in this district, 

 we have in a short distance escarpments parallel with the dip and 

 strike, and also at almost every angle to them. 



The valley is at D E about 300 yards deep, but is not shown 

 above the quarry in the diagram, as I do not allude at the present 

 time to anything more than the portion of the gravel in the valley 

 below the No. 2 vein of coal. I visited this pit several times during 

 the progress of the sinking, and counted the proportion of rolled 

 to weathered stones each time. About one-eighth of the gravel in 

 this pit was well rolled, the remainder being generally weathered. 



It is evident that if only one-eighth of the gravel is rolled by the 

 river, seven- eighths of it must have been obtained from the sides 

 of the valley, west and east of the pit, and only one-eighth from 

 the north, and that the valley was then widening much faster 

 than it was lengthening in the latter part of the Quaternary period. 

 There are times in the denudation of valleys when pluvial action on 

 the sides of the valley is much greater than fluvial action in the centre 

 of the valley. I mentioned (Quart. Journ. Geol. Soc. vol. xxiv. p. 117) 

 that even in the valley of the Somme, where the fall of the river is 

 so small, a great mass of the material deposited in the concavities 

 of the valley near the margin of the river is derived from the adja- 

 cent country, and has never been river-borne. Difierent as is the 

 position of the gravel of the Ehondda, in this respect it resembles 

 that of the Somme. 



The gravel- deposit continues for the whole length of, and is also 

 met with at a considerable height above the Ehondda river. The 



