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



They give a general indication of a southerly carry. Professor 

 Ramsay mentions the occurrence of Chalk flints in this district. 

 The author has seen them in Boulder- clay at Pendoylan, 1^ mile 

 west of Peterston, but has not traced them further west. 



The mixed Erratic district includes the Ely valley east of Peterston 

 and the land lying between it and the river Taff south of the coal-basin. 

 Besides Glamorganshire erratics, it contains, as already mentioned, a 

 few boulders, probably derived from Brecknockshire, and Chalk flints. 



The positions of these erratics, as shown in the map, indicate a 

 carry in a southerly direction ; but whether from the south-east or 

 south-west is uncertain. At Caerau there is a small group of Breck- 

 nockshire erratics ; out of seventy of the largest boulders of this group 

 examined by the author, 58 were Millstone Grit, 4 Old Red Sand- 

 stone, 4 Dolomitic conglomerate, 3 Cockshot, and 1 Carboniferous 

 sandstone. Of the Millstone-Grit boulders, 26 were subangular, 21 

 angular, and 11 rounded. From the coarseness and toughness of 

 the grit, the author thinks these erratics were derived from the 

 northern and not from the southern outcrop of the Millstone Grit. 

 This group of erratics lies between 80 and 190 feet above the sea- 

 level, and, if they were derived from Cefn-cil-sannus, are 22 miles 

 distant from their parent rocks. The fall is about 53 feet per mile. 



The largest of these erratics is a subangular cubical block of 

 coarse Millstone Grit, measuring 4| feet x 4| feet X 2| feet at least. 



The lie of the longest axes of ten large erratics, in position, does 

 not show much persistency ; three of these, however, lie with their 

 lengths 14° E. of N. and W. of S., and one of them shows a shallow 

 groove (?) on top running in the same direction. 



Chalk flints have never been seen by the author north of the 

 southern outcrop of the Coal-measures. They are tolerably abun- 

 dant on the north and south sides of the Ely valley from Cardiff 

 to Pendoylan. They have been found up to 400 feet above the sea- 

 level on the hills between Cottrell and Coed-riglan, on the south 

 side of the Ely valley. Nearly all these flints are subangular, and 

 consist of water worn (?) fragments, seldom more than two inches in 

 diameter. They occur in the Boulder-clay of the Ely valley, as well 

 as in its alluvial deposits. They are always more or less discoloured, 

 with the exception of some which have been enclosed in a compact 

 gravel underlying Boulder-clay at St. George's, 5|- miles west of 

 Cardiff. The Chalk flints in this gravel retain their original colour 

 remarkably well ; they are associated in it with a few stones foreign 

 to the neighbourhood, as quartz-porphyry, veinstone, and Lydian 

 stone. The position of the chalk flints in this gravel is shown in 

 the following section (fig. 2). No Chalk fossils have ever been 

 found by the author in Glamorganshire, nor have any traces of 

 Chalk wash been seen in its Boulder-clay. 



