406 



CONFLICTING DIRECTIONS OF THE STRATA 



where trap dislocates the strata, the points of intrusion are accompanied by conglomerates 

 and altered rocks, both resulting, doubtless, from great disturbance of the pre-existing 

 formations. 



These facts, particularly those which indicate the change of direction of the strata, 

 naturally lead us to consider the epochs when the eruptions took place. 



Conflicting directions of the strata in Pembrokeshire caused by divergent eruptions 



of Trap. 



No geologist can examine Pembrokeshire without perceiving, that its stratified masses 

 are the theatre of two great divergent lines of strike. One of these, proceeding from 

 north-east to south-west, with slight variations towards the east and west, is the same 

 which has been followed from Shropshire and Montgomeryshire to the sea cliffs of St. 

 David's. The other, trending from east and by south, to west and by north, maintains its 

 direction through South Pembroke, with the exception pointed out in Marloes Bay and 

 Skomer Island. An inspection of the map indicates the extent of country affected by 

 these divergent strikes. The first was impressed upon the strata during the accumu- 

 lation of the Cambrian and Silurian Systems, and the causes which gave rise to it, 

 continued in operation during the deposit of some of the subsequent formations. The 

 second was the result of violent movements which took place suddenly, and posterior 

 to the solidification of the carboniferous system. 



These inferences are fully substantiated by facts. In North Pembroke we have cited 

 many examples of parallel bands of trap inter stratified with the beds of sediment, showing 

 that igneous agency was in activity during long periods ; while ridges of intrusive trap 

 have heen pointed out in that district, which have burst through the same strata at a 

 later date, but upon the same parallels. In short, these two classes of volcanic matter 

 in North Pembroke, whether contemporaneous or posterior, have been emitted upon 

 lines trending from north-east to south-west, or E.N.E. and W.S.W. Such results are 

 precisely analogous to phenomena which have been described in Salop, Montgomery, 

 and Radnor ; and there can be no doubt, therefore, that not only the bedded trap, but 

 also the amorphous masses in the slates of North Pembroke (such as Trafgarn, Caer- 

 ningley, &c.) were erupted anterior to the accumulation of the carboniferous system, 

 and upon pre-existing habitual lines of eruption. 



In Shropshire it has been shown, that volcanic eruptions from north-east to south- 

 west were again in activity after the formation of the Carboniferous and New Red 

 Systems. Not so, however, in Pembrokeshire. Here, on the contrary, the carbo- 

 niferous rocks have a direction from east and by south, to west and by north, thus 

 forming an angle of at least 45° with the average axis of the older rocks. As the north- 



