CARBONIFEROUS LIMESTONE OF PEMBROKE AND STACKPOLE. 



381 



measures. In no part of the course from Milling to Poorfield is the limestone more than 50 or 60 

 feet thick. The same slender dimensions mark its course where it appears for a short distance 

 on the south side of the western coal tract near Johnston, but here it is not only much contorted 

 in the proximity of the trap rock, but also presents, at the principal quarries near Craneham, 

 the deceptive appearance above alluded to, of overlying the strata of the adjacent coal-field. 

 Powerful faults run along its escarpment from west to east in this quarter, which crossing to the 

 eastward near Langam Ferry produce the anomalies and inversions first alluded to by Mr. De la 

 Beche and of which I have already spoken. Turning, however, from these slight exhibitions of 

 the limestone at its western extremities and following it around the eastern coal-field, we find it 

 gradually expanding in a continuous mass, till it occupies a width from a quarter of a mile to two 

 miles, invariably resting upon a zone of Old Red Sandstone and dipping inwards to support the 

 great mass of the coal-field. A narrow spur of this limestone proceeds from the main zone at 

 Carew and runs from east to west terminating in Pembroke Dock Yard. This spur reposes con- 

 formably on the Old Red Sandstone of Cosheston and Hobbs Point, being troughed between the 

 latter and the ridge of Old Red Sandstone to the south of it. 



Pembroke Zone. 



The town and castle of Pembroke stand upon another band of limestone extending from Lidstip 

 on the E.S.E., where it occupies the sea cliffs for several miles, extending from Giltar Point to 

 Skrinkle Bay to West Angle Bay on the W.N.W., where its width does not much exceed a quarter 

 of a mile. This range occupies a trough in the Old Red Sandstone, and by the rise of that formation 

 is entirely separated from the limestone which supports the great coal-field. This band of lime, 

 though not exhibiting relations to the superior deposits, affords good illustrations of the structure 

 of the lower members of the formation itself and of their connection with the upper portion of the 

 Old Red Sandstone. At the eastern extremity of Skrinkle Bay, these beds with the Old Red Sand- 

 stone are vertical, and a similar junction occurs in the Isle of Caldy. 



I will not attempt to describe the numberless faults of this band of limestone, but call attention 

 simply to certain flexures not previously noticed in the eastern side of Angle Bay. The great 

 mass of the thick bedded limestone has here thinned out, being represented by only a narrow 

 band which subsides beneath the sands, but the black and flaglike sandy beds, alternating with thin 

 courses of limestone which constitute the lower limestone shale, are exhibited in two troughs, divided 

 by a ridge of Old Red Sandstone as seen in PI. 35. f. 1. 



The lower limestone shale and sandstone appear for the last time in West Angle Bay, where they 

 form a single trough in the Old Red Sandstone, the shale and impure calcareous flags being best 

 displayed on the south side, whilst a mass of good limestone is worked upon the north. 



3 B 



