Vol. 6y.] THE PEMBROKESHIRE COALFIELD. 253 



their unpublished maps and sections. In this connexion I wish 

 to express my thanks to Dr. A. Strahan, F.B.S. ; Mr. Herbert 

 H. Thomas, M.A., B.Sc. ; Mr. T. C. Cantrill, B.Sc. ; Mr. E. E. L. 

 Dixon, B.Sc. ; and also to Prof. 0. T. Jones, M.A., D.Sc. 



II. General Geology. 



The Coal Measures of Pembrokeshire occupy a belt of country 

 about 21 miles long, between Carmarthen Bay on the south-east, 

 where the coalfield is disconnected with the main coalfield of 

 South "Wales, and St. Bride's Bay on the west. In the neighbour- 

 hood of Saundersfoot the outcrop is some 4 miles wide ; but south 

 of Haverfordwest it is only about a mile wide, though it broadens 

 out again towards the coast of St. Bride's Bay. Along the northern 

 part of the eastern side of this bay there is an area of Coal 

 Measures situated to the north of the main Pembroke coalfield, but 

 separated from it by a belt of ' Millstone Grit ' and by a narrower 

 belt of rock of Bala age, both of which extend to the coast. 

 Except in the north, the strike in this area is chiefly north and south, 

 thus contrary to the general east-and-west strike of the main 

 mass of the coalfield. 



For the greater part, the Coal Measures rest on ' Millstone Grit ' ; 

 and this, between Haverfordwest and Carmarthen Bay, is followed 

 by Carboniferous Limestone. 



Roughly speaking, the eastern part of the coalfield has a 

 synclinal form, as is indicated by the fact that the lowest measures, 

 followed by the 'Millstone Grit' and Carboniferous Limestone, 

 •come to the surface both on the north and on the south of the 

 coalfield. The beds, however, lie in normal superposition only on< 

 the northern side of the basin, for in the central and the southern 

 parts the beds are complicated by inverted folds and by a large 

 number of over thrust faults. The prevailing dip in this central 

 and southern region is southwards, thus introducing an element of 

 deception along this portion of coast : for, as one approaches Tenby 

 from the north, one notes that the beds, instead of ascending in the 

 order of sequence as the direction of the dip would suggest, in 

 reality belong to lower and lower horizons. This apparent dipping 

 of the Coal Measures under the ' Millstone Grit,' and of this again 

 under the Carboniferous Limestone, is due chiefly to repeated over- 

 thrusting from the south, but also partly to inversion. 



Just as in the eastern part of the coalfield, so in the central 

 area where the coalfield is eaten into by the Eastern Cleddau, the 

 Western Cleddau, and the Daucleddau, a synclinal form can be 

 recognized. Here, however, it is less apparent than farther east, 

 the beds being still more disturbed, particularly so in the southern 

 part of this region. In this district some of the coal-seams, or 

 ' veins ' (as they are termed in Pembrokeshire), cannot be exactly 

 correlated with those that occur farther east, for considerable changes 

 have taken place. The ' Millstone Grit,' too, changes its character 



