48 



J. W. E. DAVID GLACIAL ACTION IN SOUTH 





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As all the Boulder-clay in 

 Brecknockshire examined by the 

 author is unstratified, it may be 

 provisionally assumed that it is the 

 product of land-ice. From the 

 occurrence of undisturbed sheets 

 of Boulder-clay at the bottoms of 

 valleys, as at Tstrad-fellte in the 

 Neath valley, Pen-y-graig in the 

 Rhondda-fawr valley, and St. Fa- 

 gans and St. George's in the Ely 

 valley, it may be inferred that the 

 excavation of these valleys took 

 place at some time previous to the 

 final disappearance of the ice. 



3. Shattered and contorted Bock- 

 surfaces and intrudedBoulder-clay . 

 — The rocks of South Brecknock- 

 shire and East Glamorganshire, 

 which are soft and easily disjointed, 

 are more often shattered and con- 

 torted than striated. This is the 

 case in the Old Eed Sandstone 

 area south of the Beacons, and 

 with many of the finely laminated 

 sandstones of the Coal-measures 

 and the Triassic and Liassic rocks 

 of the Ely valley. 



This shattering and contorting 

 of rock-surfaces is much more 

 common as an evidence of glacia- 

 tion in the coal-basin than the 

 grooving and striating of the sur- 

 face-rock. It is to be met with 

 everywhere, on the north, north- 

 western, and north-eastern slopes 

 of the Carboniferous-sandstone 

 hills. In the Ely valley this rock- 

 shattering is particularly well 

 marked in the rocks belonging to 

 the Lower Lias formation. At Ty- 

 fry, near St. Fagans, there are seve- 

 ral roches moutonnees, which illus- 

 trate the contorting and crushing 

 power of ice and the intrusion of 

 Boulder- clay. At Ty-fry, where 

 a quarry has been opened in two 

 of these roches moutonnees, the 

 rock has been so much crushed as 

 to form a fine angular breccia, 



