227 



expose the formations of which it is composed in descending order 

 from the coal-measures to the Cambrian System. The points of 

 novelty in the descriptions of the author apply to the persistence of 

 the carboniferous deposits along the coast of St, Bride's Bay, where 

 they are not separated by any mass of greywacke as indicated in 

 former maps, the parts producing culm*, lying simply to the N. 

 and S. of a highly dislocated promontory of carboniferous grit. 

 The contortions and innumerable faults of these coal-measures being 

 pointed out, attention is then called to some of the probable results 

 of such movements in the singular accumulations of finely fractured 

 stone coal in small basins called "slashes," and to other vertical 

 downcasts of the mineral termed " sloughs." The shale of these culm 

 deposits resembling in some respects certain strata of the upper Si- 

 lurian rocks, might to an unpractised eye appear undistinguishable; 

 but even where the order of superposition is'not tobe detected, essential 

 differences are invariably to be observed, in the coal shales never con- 

 taining those organic animal remains which are so abundant in the 

 Silurian system, whilst the latter never contains a single plant simi- 

 lar to those which abound in the former. Instances are cited where 

 by dislocations the coal measures are thrown into positions apparently 

 conformable to old greywacke rocks of the Cambrian system, and 

 hence the author surmises, that if the millstone grit and carboniferous 

 limestone were not present in many adjoining parts to test the true 

 age of these coal measures, mistakes might easily result from such 

 juxta-positions. Cherty and siliceous sandstones (the millstone grit) 

 rise in dome shapes to the west of Haverford, and occupy large por- 

 tions of the coal tract underlying the productive culm measures and 

 capping the mountain limestone. 



Carboniferous Limestone. — In this formation, besides the very ac- 

 curate outline expressed in Mr. De la Beche's mapf, the author re- 

 marks the existence of a double trough of the lower limestone shale 

 overlying the old red sandstone in East Angle Bayj and he particu- 

 larly adverts to the peculiar mineral character of these beds in Pem- 

 brokeshire in containing yellow and light coloured sandstones alter- 

 nating with shale. The fossils of this lowest member of the carboni- 

 ferous system are numerous, many having been furnished by the Earl 

 of Cawdor ; and as far as they have been yet examined they appear to 

 differ specifically from all the fossils of the inferior systems. The coal 

 measures and mountain limestone of Pembroke are singularly subject 

 to great faults ; one of the most remarkable of which occurs between 

 Johnston and Haverfordwest, where the carboniferous limestone is 

 thrown into a position by which it appears to overlay the coal. 



Old Red Sandstone. — The upper strata of this great formation pass 

 upwards in many places into the shale and sandstone of the carboni- 



* All the coal of Pembroke is stone coal, and it is usually in the laminated 

 condition of culm. 



t The survey of the county was much facilitated by the possession of Mr. 

 De la Beche's map of South Pembroke, which, though differing in some 

 points from that completed by the author, is mentioned by him as a work of 

 great merit for the period of its publication. 



