Ch. XIII.] THE INCLINED POSITIONS OF STRATA. 277 



De la Beche, in his description of southern Pembroke- 

 shire *, states, " that the trap of this district, which is generally 

 associated with and subjacent to greywacke, such as would 

 formerly be termed transition-trap, supports contorted beds 

 of old red sandstone, at Millhaven, and is incumbent on 

 carboniferous limestone and coal-measures at Goultrop Head." 

 " It would be difficult," he adds, " to explain these pheno- 

 mena by any other hypothesis than that of the forcible intru- 

 sion of trap among the other rocks, at a period subsequent to 

 that of their being formed and consolidated." The question, 

 however, for our more immediate consideration, is the dip of 

 these strata near the trap, which this excellent observer 

 informs us is generally very elevated, and sometimes perpen- 

 dicular. The bearings or strikes of these ranges of trap 

 appear to correspond with those of the strata : thus, in the 

 southern part of the district, the bearings of both are nearly 

 E. and W., the strata dipping for the most part towards the 

 south : in the northern part the trap of Pencarnon is about 

 N. and S., and the strata, on the western side, dip to the W., 

 " varying N. and S., conformably to the trap range which 

 stretches from Crosswoodig." As regards the amount of dip, 

 between the trap ridges of Cesselvawr and Llacithty, the beds 

 of greywacke are perpendicular ; immediately south of the 

 latter they are also perpendicular; thence to Cuffern range 

 they dip towards the south, as they do also on the southern 

 side of the same range ; they are nearly vertical at Guildford, 

 north of the trap range of Bolton, whilst they dip on the 

 opposite side of the range, towards the south, at various 

 angles, varying from 20 to 50 ; the strata of greywacke, on 

 the south side of the wedge-shaped mass of trap, at Marloes, 

 dip S., and of the red sandstone, on the northern side of 

 the same, have a like inclination, both rocks dipping at con- 

 siderable angles ; and, as the breadth of the trap diminishes, 

 these rocks gradually approach each other. If, then, the 



* Geol. Trans. (New Series), vol. ii. p. 1. 

 T 3 



