Vol. 52.] GEOLOGY OF THE NEIGHBOURHOOD OF CARMARTHEN. 525 



frequently crop out along north-and-south lines for a short distance, 

 as is well seen in Mr. Roberts's district to the west. After this 

 universal crumpling of the crust had taken place a second period of 

 folding on a still grander scale set in. This was evidently part of 

 that great movement which produced the Condrozian ridge, and all 

 the beds of this part of Wales were affected by it. In the end a 

 great series of huge anticlines and synclines were formed with their 

 axes running east and west, so that the second movement was at 

 right angles to the first. A single limb of one of these complex 

 anticlines forms the subject of the present paper. The uniform 

 direction (N. to N.W.) of the cleavage throughout the district shows 

 that it was produced either simultaneously with this last folding or 

 at a later period. 



III. The Succession and Detailed Description of the Beds. 

 1. Tremadoc Slates. 



About 2| miles south-west of Carmarthen, exposed in the banks 

 of the Nant-y-Glasdwr, are fine-grained blue-grey shales, which 

 weather a rich yellow or brown, and are often iridescent. Inter- 

 calated with the shales are occasional bands of micaceous sandstones. 

 The beds dip 68° due south, and pass immediately under the Old 

 Red Sandstone. They have yielded Ogygia marginata, n. sp., 

 Parabolinella, n. sp., Peltura punctata, n. sp., Orthis, and Orthoceras. 

 Peltura punctata occurs very abundantly, Ogygia marginata 

 much less frequently, and only one specimen of Parabolinella was 

 obtained. 



Confirmatory Sections. 



A little west of the Nant-y-Glasdwr, in the Nant Pibwr at Cwm 

 Ffrwd, the shales are more gritty, and assume the character of 

 mudstones. Alternating with them are some hard grey grit-bands. 

 The junction with the Old Red Sandstone is seen in the bed of the 

 stream, and near it the shales are considerably disturbed, the dip 

 varying repeatedly in the space of a few yards ; elsewhere the dip 

 is south. We found here Ogygia marginata, Peltura punctata, 

 Orthoceras sericeum, Salt., and Modiolopsis. The Ogygia occurs 

 much more plentifully here than in the Nant-y-Glasdwr, but no 

 perfect specimens were obtained. On the western side of the 

 River Towy near Cwrt Hir Farm, in a hole by the roadside, we found 

 fragments of Erinnys, sp., Peltura punctata, and Orthis-, and a 

 little east of this, in Cwrt Hir carriage-drive, where there is an 

 alternating series of coarse grits and shales, we found in the shales 

 Ogygia marginata and a species of Orthis. 



2. Arenig Beds. 



A typical section of these beds is seen just below Glan Pibwr 

 Cottage, in the narrow lane which leads down to the stream. They 

 consist of fine-grained, dark, bluish-grey mudstones, finely bedded, 

 and weathering in iridescent shades of brown and red. The rock 



