SILURIAN ROCKS IN FRESHWATER, EAST AND WEST. 



391 



sandstone, whilst at Milling the Asaphus caudatus and other fossils would indicate that the shale 

 which abuts against the carboniferous limestone is of the age of that of Wenlock. 



Let us now view these rocks as presented on the coast. In the southern or Pembroke promon- 

 tory they rise in highly inclined strata from beneath the Old Red Sandstone, appearing in the bay of 

 Freshwater east, whence they traverse to Freshwater west, thus at each extremity of the promontory 

 occupying a bay of about one mile in width. Another spur of these rocks is prolonged from Fresh- 

 water west along the valley of Castle-martin-gorse, to the pleasure grounds north of Stackpole Court, 

 where a fossiliferous sandstone subsides beneath the Old Red Sandstone. At Freshwater east, where 

 the relations are clear, the Old Red Sandstone is thrown up on both sides into so highly inclined 

 positions, that the Silurian rocks are better exposed. At the eastern side of this bay, the junction is 

 obscured by blown sands, and there is probably a fault, though some of the beds of Old Red Sand- 

 stone, consisting of yellow and greenish sandy flags with red way-boards, dip off 70° to the north, 

 the strike of the strata being 10° north of west. The inclination of the Silurian rocks increases to 

 the centre of the bay, where beds of sandstone charged with fossils rise out at the back of the hills 

 of loose sand in almost vertical positions, whilst in the western cove on the other side of the bay, in 

 approaching the contact with the Old Red Sandstone, beds of dull greenish grey sandstone with little 

 or no mica and with a few casts of fossils dip to the south-west at 45° or 50°. 



From this spot the Earl of Cawdor procured the following remains, — Leptcena depressa ? (imper- 

 fect cast of) Leptcena rugosa, Spirifer (sharp plaited species), Atrypa twnida? Dalm., Cucullcea 

 Cawdori, N. S. The last named shell, being the first example of that genus found in a rock of so 

 high antiquity, I have named it after its discoverer. A small species of trilobite also occurs, and 

 it is essentially different from any form known in the carboniferous limestone. (See PI. 35. f. 12.) 

 The overlying beds consist of a grey conglomerate of coarse angular fragments of Silurian rocks 

 with rounded quartz pebbles, and plunge under the red sandstone. 



This spot is the scene of faults, since the strike of the Silurian beds is 35° north of west and 35° 

 south of east, and that of the Old Red is 10° west of north with a dip to the west. The coarse 

 conglomerate in the Silurian rocks is not however confined to this locality, for it sweeps in a strong 

 band along the flanks of the Old Red Sandstone, passing by Thurtle Mill and Dry Barrows on the 

 west, and reappearing from beneath the blown sands of Newton Barrows, it runs out in strong ledges 

 in the northern side of the bay of Freshwater west. Similar relations of this coarse grey conglo- 

 merate are seen in the northern side of the valley of Castle-martin-gorse, near Corston House 

 and Stem Bridge, and it may, therefore, be recognised as marking the edge of the Silurian rocks 

 through this tract. Though we find traces of the Silurian rocks on each side of the bay of Fresh- 

 water west, similar to those mentioned at Freshwater east, exposed at low water and dipping to 

 the north and south at high angles beneath the Old Red Sandstone, the underlying beds which 

 once occupied the centre of this bay have been denuded. 



The coarse conglomerate here mentioned, must not be mistaken for the conglomerate which in 

 Pembrokeshire, occurs in the lower division of the Old Red Sandstone, the pebbles in which are 

 smaller and more rounded, and its matrix similar to that of all the red sandstone conglomerates. 

 Nor are these Silurian conglomerates which rise up in narrow belts through the Old Red Sandstone 

 between Freshwater east and Freshwater west of great extent, for in the full development of the 

 Silurian System in Marloes Bay, which I now proceed to describe, there is no trace of them. 



3 c2 



