Mr. De la Beche on the Geology of Southern Pembrokeshire. 6 



crystals of a green colour, crystallized felspar, and very little quartz. At the 

 tor of Clegurfwya, and at other points to the west of St, David's, the rock 

 resembles that of Treginnis, described by Dr, Kidd (see Geological Transac- 

 tions, first series, vol. ii, p. 89.) as "assuming the appearance of compact earthy 

 felspar, being of an oUve-green colour, and probably containing epidote." A 

 section of this body of trap extends along the coast from the point opposite the 

 Horse Rock in Ramsey Sound, to Pen-y-Main-Melin Point, and thence to the 

 point opposite the rocks called the Bishops and the Crow, 



The two irregularly conical hills called the Beacons of Ramsey, the one 

 on the northern, the other on the southern side of the island, are composed of 

 trap. The northern beacon consists principally of greenstone, resembling 

 that of the ridge of Llacithty, On the west it is bounded by the sea, but on 

 every other side by strata of greywacke, A bed or dyke of cornean occurs 

 between the vertical beds of greywacke that separate the two beacons, having, 

 like those beds, a direction from east to west. The southern beacon, together 

 with Margery Isle, and so much of Ramsey Island as lies to the south of a 

 line drawn from near the House to the southern end of Abermawr Sand, con- 

 sists chiefly of porphyry. Felspathic and quartzose cornean are associated 

 with the trap on this side of the island. A substance resembling anthracite is 

 found in vertical veins traversing the trap of the southern part of the island. 

 Wherever it is exposed to the sea, it is washed out, and the walls of trap are 

 left standing, forming picturesque coves. 



It would be difficult to determine accurately, owing to the want of natural 

 sections, how much of the surface immediately around St. David's consists of 

 trap. Blocks of it, belonging principally to the greenstone variety, lie scattered 

 over the soil in every direction, and are often seen resting upon greywacke. 

 At Clegir Bridge, near St. David's, quartzose cornean, occasionally striped, 

 is found associated with greenstone. Following the high-road from thence 

 to Solfach, almost all the field-divisions are found to consist of blocks of trap. 

 Some few, of large dimensions, which have not been thus appropriated, are 

 observed resting on greywacke, which is here the prevailing rock. Trap 

 occurs intermixed with greywacke in the neighbourhood of Solfach, It is 

 found in ascending the hill on the road to Haverfordwest, Porphyritic 

 greenstone is met with under Upper Solfach, Both the points of Solfach 

 Harbour are composed of greenstone, which may be traced across two or three 

 small headlands to the eastward, there forming a vertical bed or dyke not 

 more than a few yards in thickness, having the same direction as the ver- 

 tical beds of greywacke, and probably interposed between them. Pursuing 

 the high-road from Solfach to Newgate Bridge, the blocks in the field-divi- 



