BKECXNOCKSHIKE AND EAST GLAMOKGANSH1BE. 41 



The whole of this area has a moutonnee aspect : the outlines of 

 nearly all the hills are smooth and flowing, while drums, sow-backs, 

 and troughs are noticeable features, especially on the south side of 

 the Ely valley. Roches moutonnees are of frequent occurrence in 

 Brecknockshire, in the Old Red Sandstone, Carboniferous Limestone, 

 and Millstone-Grit areas, but are rarely met with in the Coal-basin 

 or Ely valley ; they are fairly well developed, however, on the Car- 

 boniferous sandstone at the top of the Avon Dare valley, near Aber- 

 dare, on the Millstone Grit at Cefn Hirgred, near Bridgend, and on 

 the Lower Lias limestone at St. Eagans, near Cardiff. Contorted 

 bedding in drift is well shown in the cutting on a new line of rail- 

 way at Craigau, near Llantrisant. 



The four other kinds of evidence must be described in detail. 

 These are: — 1. Erratics; 2. Boulder-clay; 3. Shattered and contorted 

 rock-surfaces; 4. Grooved and striated rock-surfaces. The first 

 three obtain everywhere in this area, whereas grooved and striated 

 rock-surfaces are confined, so far as the author is aware, to the sand- 

 stones of the coal-basin, north of Maendu, near Treforest in the 

 Taff valley, to the Millstone Grit at its northern outcrop from the 

 Coal-measures, and to a small extent of Carboniferous Limestone 

 cropping out to the north of this Millstone Grit. 



1. Erratics. — All the erratics are of local origin, with the exception 

 perhaps of the chalk flints of the Ely valley, and possibly of a small 

 block of quartz-porphyry found in an old wall at Duffryn Golwg, St. 

 Nicholas, Cardiff. 



The area of their dispersal extends 29 miles from the Beacons to 

 the southern water-parting of the Ely valley, between Cardiff and 

 Cowbridge, very few erratics occurring south of this watershed. 

 Eastward they have been traced by the author to the Rhymney 

 and Taff-fechan valleys, and westward to a line drawn from Cow- 

 bridge to Ystrad-fellte, in the Neath valley. Thus the erratic area 

 forms a wedge-shaped tract of country, 8 miles broad at its northern, 

 and 15 miles at its southern limit. 



The erratics are composed of angular, subangular, and rounded 

 blocks of Old Red Sandstone, Carboniferous Limestone, Millstone 

 Grit, Carboniferous sandstone, and Cockshot as far south as the Coal- 

 measures. South of this line they are found associated with boulders 

 derived from the Triassic and Liassic formations, and with sub- 

 angular fragments of Chalk flints. 



The greatest height of the Old Red Sandstone erratics above the 

 sea-level is from 1400 to 1500 feet; that of the boulders derived from 

 the Carboniferous Limestone and Millstone Grit from 1200 to 1300 

 feet ; that of the erratics of Cockshot and Carboniferous sandstone 

 from 700 to 800 feet. In the Ely valley boulders derived from the 

 Trias and Lias seldom occur higher than 300 feet above the sea-level. 

 Erratics derived from all these formations are to be found in the 

 Ely valley as low as within 50 feet of the sea-level. 



The area of the dispersal of the erratics, north of the southern 

 outcrop of the Coal-measures, may be conveniently divided into two 



