YELLOW AND GREY VARIETIES OF OLD RED IN PEMBROKESHIRE. 385 



stone) cannot be sustained ; a fact naturally to be expected, when it has already been 

 shown that such distinctions are not maintained in the southern part of Caermarthenshire. 

 2nd. Although the rocks are for the most part of a red colour {red rab 1 ), there are con- 

 siderable tracts where they consist of grey and sometimes of yellowish sandstone. 



Near Tavern Spite, where it enters Pembrokeshire, the Old Red Sandstone is thrown out into a 

 promontory at Cynic, the escarpment of which, as it rests against the Silurian rocks, trends from 

 north-east to south-west, whilst the upper member of the same mass folds round to the south-east, 

 encircling and dipping under the carboniferous limestone and coal measures of Amroth and Tenby. 

 This mass of Old Red, taking an east and west direction and tapering away in its course to the 

 west, wedges out and disappears at the eastern end of Mynwer Wood, on the left bank of the river, 

 opposite to Slebech. This is the only large development of Old Red Sandstone which lies to the 

 north of the great coal-field. All the other districts occupied by this rock are to the south of 

 it ; either immediately underlying the coal bearing strata between Tiers Cross and Rosepool in the 

 western district, or accompanying and supporting the carboniferous limestone in long continuous 

 ridges. Examples have been already cited, where the overlying limestone passes down into this 

 formation, and we may now state, that the lower members graduate into and repose upon strata of 

 the Silurian System. (See PI. 35. f. 6.) 



The upper part of the system which graduates into the lower limestone shale, as seen at Sawdorn 

 in East Angle Bay, consists of the ordinary, dull red, argillaceous shale, provincially termed " red 

 rab," alternating with courses of grey and greenish, flaglike sandstones. These are underlaid by 

 other beds of the red rab, containing subordinate thick strata of quartzose red conglomerate, the 

 pebbles being occasionally of the size of a man's fist. I have not observed these conglomerate beds 

 in many other parts of South Pembrokeshire, though they are here precisely in the same situation 

 in which they occur in parts of Monmouthshire and Gloucestershire, where they are separated from 

 the overlying limestone by courses of red and grey sandstone, shale, &c. (PI. 35. f. 1.) 



In a section recently laid bare between Hobbs Point and the narrow spur of limestone of Pembroke 

 Dock, the upper members of the formation are composed of thin, flaglike, reddish, sandy shale, pass- 

 ing down into grey and purple, hard, micaceous sandstone, the ordinary dull red rab re-occurring at 

 intervals. A similar succession is observable in all the transverse sections from this Pembroke band 

 of limestone to the promontory of Cosheston, for though the prevailing sandstones are yellow, they 

 alternate with red rab under Cosheston Church and pass conformably under the carboniferous lime- 

 stone. The same peculiarities of colour may be equally seen in the northern district, south of Cold 

 Blow, where courses of yellow sandstone of considerable thickness alternate with red rab, but the 

 former so exceeds the latter in quantity, that the yellow colour prevails over the red, in a great breadth 

 of surface. In most of these cases, however, zones of red rock are interposed between the yellow 

 sandstone and the lower limestone shale. 



These yellow and grey sandstones occupy a considerable area in other places ; as in the greater 

 part of the promontory of Cosheston, with the western bank of this part of the Milford estuary, 

 occupying Williamston Mountain and Burton parish. The sandstone is generally flaglike and 

 micaceous on the surface of the laminae, and sometimes contains green blotches of marl, and very 

 rarely a few fragments of carbonaceous matter. The beds are frequently of a foxy, yellow colour, 

 and decompose to a sandy, sterile soil, which as it exhibits very few traces of red rock, might lead 



1 "Rab" is sandy shale. 



