160 ME. F. BIXEX AXD PROF. T. F. SlBLX OlS' THE [vol. Ixxiii, 



Plate XIII. 



Fig. 1. The gorge of the Taff below Taff's Well: view looking 

 south-eastwards from the eastern end of Garth Hill. The gorge 

 separates the Carboniferous-Limestone ridge of Fforest Fawr on 

 the east from that of Garth Wood on the west (map. PI. XVI). 

 The wooded dip-slopes of these two ridges appear in the picture. 

 Beyond Fforest Fa^\'r is seen the ridge of Greenmeadow Wood, 

 determined by a quartz -conglomerate at the base of the Upper 

 Series of the Old Red Sandstone. In the foreground, the Taff 

 valley widens in the strata of the Millstone Grit and the Lower 

 Coal Series, and receives a tributary strike -valley, cut in these 

 strata, from the west. In the distance, the limestone-gorge opens 

 out into the lowlands of Old Red Sandstone which extend south- 

 wards to Cardiff. Cwarre Glas lies in the Seminida Oolite (p. 147). 

 The quarries and cuttings on the eastern side of the gorge expose 

 almost the whole of the Carboniferous Limestone Series (pp. 128, 

 130. 131, & 149-51).— F. Dixey, photo. 

 2. The escarpment of the Main Limestone, Garth Wood: 

 view looking Avestwards, across the southern end of the Taff gorge, 

 from the hill above Tongwynlais (map, PI. XVI). Ty-nant Quarry 

 (pp. 136 & 138) is seen at the foot of the escarpment. The 

 Lower Limestone Shales lie buried under drift at the foot of the 

 escarpment. — F. Dixey, photo. 



Plate XIV. 



General view of a quarry in C.,-Sj beds, a quarter of a mile 

 north of Miskin. This quarry (Glam. 42 NW A 2) illustrates 

 the sequence of the three groups, 10, 11, & 12. recognized in the 

 standard limestones of C, and S^ near Miskin. (See p. 144.) 

 T. F. Sibly. photo. 



Plate XV. 



Geological map illustrating the Carboniferous Limestone Series between the 

 Ewenny valley and the Taff valley, on the scale of 2 inches to the 

 mile, or 1 : 31,680. 



Plate XVI. 



Geological map illustrating the Carboniferous Limestone Series between the 

 Taff valley and the Ebbw valley, on the scale of 2 inches to the 

 mile, or 1 : 31.680. 



Discussion. 



Dr. A. Stkahax expressed the pleasure with which he saw the 

 details being tilled into the outlines which he and his colleagues 

 had drawn many years ago. . Part of the outcrop described by the 

 Authors presented exceptional difficulties, for the lithologieal types 

 Avere abnormal and fossils were scarce. It would be interesting to 

 see how zones had been mapped under such conditions. It had 

 been known from the first that the limestone series became greatly 

 diminished in thickness from south to north or noi-th-east ; and it 

 had long been a jnatter of discussion how far this was due to an 

 originally meagre development, and how far to overlap by the 

 Millstone Grit. There are, in places, indications of erosion of the 

 limestone-surface below the basal conglomerate of the Millstone 



