52 J. W. E. DAVID GLACIAL ACTION IN SOUTH 



Their trend is 47° E. of S. ; height above the sea-level, as taken by 

 aneroid, abont 1320 feet ; fall from the Beacons, 15 miles distant, 

 106 feet per mile. Bearing nearly due south from Gelligaer Common, 

 5^ miles distant, there is a faintly grooved flat surface of Carboni- 

 ferous sandstone, near Cwm Sarn, on the south-east spur of the 

 Eglwysilan mountain. Their trend is about 9° E. of S. ; height 

 above the sea-level 980 feet ; fall from the Beacons, 29| miles distant, 

 about 94 feet per mile. 



Bearing nearly due west from Cwm Sarn, 3| miles distant, there 

 are well-marked grooves on a mamillated surface of Carboniferous 

 sandstone, near the " Rocking-stone," Pont-y-pridd. The impact- 

 surface ("Stossseite") of this hill, as of most of the hills in the coal- 

 basin, is too much shattered to show striae. The trend of the grooves 

 here is about 7°E. of S., or nearly parallel to the grooves at Cwm Sarn ; 

 height above the sea-level, as taken by aneroid, 360 feet ; fall from 

 the Beacons, 19 1 miles distant, about 131 feet per mile. Passing 

 now to the Khondda valley, west of the TaflP valley, faint striae are 

 discernible on a faintly ground surface of Carboniferous sandstone, 

 near Pen-y-graig, in the Rhondda-fawr valley. Their direction is 

 from 30° to 40° E. of S., foUowing the trend of the valley. Their 

 height above the present level of the valley-bottom is about 40 feet. 

 They bear 68° W. of N. from the striae near the " Rocking-stone," 

 5| miles distant ; distance from the Becaons 18 miles. 



Bearing nearly due east of the Pen-y-graig striae, 4| miles distant, 

 between Cefn and Lan farmhouses, a mamillated surface of Car- 

 boniferous sandstone has been exposed from under some rubble in 

 making a road. This is grooved and striated in a direction about 

 33° E. of S. Its height above the sea-level, as taken by aneroid, is 

 555 feet ; distance from the Beacons 18| miles ; fall about 127 feet 

 per mile. 



Bearing 17° W. of S. from the " Rocking-stone " striae, f mile 

 distant, are some faint striae on a rounded surface of Carboniferous 

 sandstone, running 26° E. of S. ; height above the sea-level, as 

 taken by aneroid, 482 feet ; distance from Beacons a little over 20 

 miles ; fall about 128 feet per mile. Bearing 8° W. of S. from this 

 last point, one mile distant, an extensive striated surface of Carboni- 

 ferous sandstone has recently been exposed from under a covering of 

 Boulder-clay from 5 to 6 feet thick, at Haendu quarry, near Treforest. 

 Trend of striae nearly due N. and S. ; surface flat, height above 

 the sea-level 705 feet. 



This is the southernmost point in the whole area at which the 

 author has seen a striated rock-surface. The distance from the 

 Beacon is 21 miles ; fall 105 feet per mile. 



Summary. — It would be premature for the author, in the present 

 imperfect state of his knowledge, to attempt to systematize all these 

 glacial phenomena ; as, however, a few points seem already esta- 

 blished, it may be well to state them. 



I. The erratics in the Eglwysilan and Caerau group were pro- 

 bably transported by floating ice. This is implied (1) by the 



