Mr. De la Beche on the Geology of Southern Pembrokeshire. 11 



red-coloured beds : at the village on the eastern side it has much the appear- 

 ance of slaty old red sandstone. Between Guilford and the trap are brownish- 

 gray beds, having the aspect of greywacke, mixed with others that resemble 

 old red sandstone. At the bottom of Benton Wood these beds are nearly ver- 

 tical. 



Similar rocks to the preceding occur to the south of the trap near Marloes. 

 They consist either of coarse slate, or of beds very variable in thickness. 

 Thick beds of very compact quartzose sandstone are found resting on the trap 

 to the south of St. Martin's Haven, and dipping to the south at from 45° 

 to 50°. 



A section drawn southwards, from the trap of Gouldtrop Road at Talbanny 

 »to St. Ann's Head, shows that these beds, which so much resemble grey wacke, 

 are intimately connected with old red sandstone. The dip of all the beds in 

 this section is to the south, generally at a high angle. From Talbanny to 

 Mallock Mill we have genuine old red sandstone. At the latter place appear 

 some beds resembling greywacke. To these succeed others of old red sand- 

 stone. Near Marloes the pseudo-grey wacke recurs, and continues to the coast 

 opposite Gateholm Island. The coast and the island are of old red sandstone. 

 Similar alternations are seen in the cliffs between Little Marloes and St. Ann's 

 Head. 



§ 3. — Old Red Sandstone. 



The old red sandstone of Pembrokeshire, like the greywacke, may be con- 

 sidered as forming two principal districts ; the first lying to the north, the 

 second to the south, of the Coal-basin. 



(A) Old Red Sandstone to the North of the Coal-basin. 



This district, forming the western extremity of that connected tract of old 

 red sandstone which traverses the counties of Hereford, Brecknock, and Gla- 

 morgan, lies eastward of that branch of Milford Haven which reaches up to 

 Canaston Bridge, and receives the Cledden or East Cledder river. From 

 Mynwer its southern boundary passes nearly due east, by Templeton and 

 Pendine, to Caermarthen Bay. Its junction on the north with greywacke, 

 between Canaston and Lethergloyn, has been already noticed. 



This sandstone along its southern boundary dips to the south, at an angle 

 of from 20° to 25°; but to the north of this boundary the angle increases con- 

 siderably. 



(B) Old Red Sandstone to the South of the Coal-basin. 



This southern district is subdivided into three minor ones ; that of Milford, 



c2 



