720 



DESCRIPTION OF THE SECTIONS. 



the Old Red Sandstone, and from the latter into the Upper Silurian Rocks. The greater part 

 of this section is exposed on the banks of the river Sowdde, which flowing in a rocky channel 

 affords a clear view of the cornstones and tilestones, and the junction of the latter with the 

 equivalent of the Ludlow Rocks (at Pont-ar-lleche, or the bridge upon the tilestones) . The trap 

 of Blaen-dyftrin-garn, on the left bank of the Sowdde, penetrates the Lower Silurian Rocks. 

 See pp. 175, 182, 348 and 355. 

 Fig. 6. From the Millstone Grit and Carboniferous Limestone of the South Welsh coal basin to 

 the banks of the Towy, north of Llandeilo, exposing the relations of the outlier of Carbonife- 

 rous Limestone called Castell-cerrig-cennen, and the Silurian Rocks in vertical and closely 

 compressed masses. 



The Llandeilo Flags are well exposed, and a band of Caradoc Sandstone is interposed be- 

 tween them and the Upper Silurian Rocks. 



Fig. 7' From the Millstone Grit and Carboniferous Limestone of the South Welsh coal basin, near 

 the sources of the Lwchor, to the hills north-west of Llandeilo, principally to exhibit a full 

 succession of the Llandeilo flags with stony beds of limestone near the lower limits of that for- 

 mation (Griig). See pp. 349 et seq., 355 et seq. 



Fig. 8. Transverse section from south-east to north-west (similar to figs. 6 and 7-)j from Llandibie 

 in the South Welsh coal-field, to the hills of Aberglasslyn on the right bank of the Towy ; 

 showing a thin zone of Upper Silurian Rocks rising from beneath the Old Red Sandstone near 

 Golden Grove, and a full extension of the Lower Silurian (principally Llandeilo flags) between 

 that place and Aberglasslyn. To the north-west of Aberglasslyn is a passage downwards from 

 the base of the Llandeilo flags into crinoidal grits, and shale or beds intermediate between the 

 Silurian and Cambrian Systems. (The river Towy flows in a great longitudinal denudation.) 

 See pp. 355 et seq. 



Fig. 9. From the Millstone Grit and Carboniferous Limestone of Llangyndeyrn to the hills of Cam- 

 brian schist, north-west of Caermarthen, showing a small zone of Upper Silurian Rocks, and a 

 peculiar band of Lower Silurian schist on the left bank of the Towy, with fossils of the Llan- 

 deilo flags. See p. 358. 



Fig. 10. Arch of cornstone in the Old Red Sandstone at Llanstephan Castle, near the mouth of 

 the Towy. See p. 176. 



Fig. 11. Traverse from the Old Red Sandstone to the Cambrian schist, a few miles south-west of 

 Caermarthen, showing a line of fault along the junction of the Upper Silurian Rocks with the 

 Old Red, accompanied by outbursts of trap and a peculiar mineral development of the Silurian 

 System. See p. 366. 



PLATE 35. 

 (Pembrokeshire.) See pp. 370 to 408. 



Fig. 1. General transverse section across Pembrokeshire from Pennyholt Stack on the south to 

 Fishguard on the north, exposing the formations in descending order from the Carboniferous 

 Limestone to the slaty rocks of the Cambrian System, with a broken trough of cumi mea- 

 sures, numerous protrusions of trap, and many dislocations of the strata. 



In this section the Silurian Rocks are ill exposed, and in the neighbourhood of Haverford- 

 west only. The Cambrian Rocks exhibit in one part the peculiar phenomenon of a coincidence 

 between the laminae of deposit and the lines of slaty cleavage. 



