Vol. 68.] PRE- CAMBRIAN AND CAMBRIAN OF PEMBROKESHIRE 393 



The Ford Beds. 



The position of the Ford Beds in the Cambrian sequence is by 

 no means clear. 



(6) The lowest beds are exposed in the railway-cuttings to the 

 south-east of Musland, and consist of about 50 feet of greenish- 

 yellow felspathic grit which forms rather thick beds. The central 

 portion is somewhat coarse and pebbly, while at its upper limit it 

 passes up into the overlying shaly and flaggy series. To the same 

 grit may be assigned the numerous blocks of pebbly grit on each 

 side of the road, half a mile west of Ford ; it is there followed by 

 the shaly group. 



(7) As exposed in the deep railway-cuttings, the upper group 

 consists of greenish-blue of dark-blue shales, with numerous thin 

 pale bands which resemble ashy layers ; iron-pyrites is of frequent 

 occurrence in some of the beds. 



The group is traversed by a persistent cleavage, which makes 

 a small angle with the bedding. On weathering, the beds appear 

 as soft buff-coloured or whitish shales : they are usually somewhat 

 striped, their joint-faces are often stained yellow with iron, and are 

 sometimes iridescent. 



Curious tube-like markings occur on some of the surfaces, and 

 are suggestive of annelid borings. But, despite assiduous search, no 

 fossils have been found in this group. 



Pale greenish highly-cleaved shales also succeed the green 

 quartzitic sandstones (5) in an old mill-leat north of Welsh 

 Hook ; they resemble the Ford Beds very closely. In this section 

 they appear to pass up conformably into very dark shales of the 

 Menevian type, but these rocks are so inaccessible that they cannot 

 properly be searched for fossils. 



It is not known upon what the base of the Musland Grit rests 

 in the railway-cutting ; but, if no fault occurs along the bed of the 

 river in that locality, it would appear that a small thickness of 

 the upper green sandstones intervenes between the purple sand- 

 stones and the Musland Grit. 



Beds Nos. 1-4 can be paralleled readily with various subdivisions 

 of the Caerfai Group of Hicks : the correspondence is closer 

 than would appear from published accounts of the St. David's 

 sequence, for the thickness of some of the subdivisions, notably the 

 purple Caerbwdy Sandstones, was overestimated by Hicks. The 

 red shales (ISTo. 3) correspond to those which yielded fossils near 

 St. David's, and, like them, contain a thin bed of felspathic tuff. 



Succeeding the purple Caerbwdy Sandstones in the St. David's 

 district are the basal beds of the Solva Group ; it is difficult to 

 determine, however, where the dividing-line was supposed to be 

 drawn. The group which conformably succeeds the purple sand- 

 stones to the west of Caerbwdy Bay closely resembles the green 



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