Geological Society. 565 
observations of Prof. Sedgwick, because if strictly scrutinized the 
phenomena are not placed in opposition to them, since it was his 
belief upon the spot, that the crystallizing action which gave to these 
masses their hard slaty properties produced the flaglike lamine of the 
beds. 
Trap Rocks.—Of these there are distinctly two classes: 1, Bedded, 
and synchronous with the formation of the older rocks’; 2, Posteriorand 
intrusive. Of the former there are no examples like those cited in West 
Salop, Montgomery, and Radnor, (see former memoirs,) of alternation 
with the strata of the Silurian system, being all confined to the Cam 
brian rocks. The tract extending from Fishguard to St. David’s and the 
Isle of Skomer offer illustrative examples of both these classes of trap. 
In addition to the varieties of sienite, compact felspar rock (corneen 
of De la Beche), greenstone, &c., of which these rocks are composed, 
the author has detected crystallized chromate of iron and albite in St. 
David’s Head,—small veins of copper ore also occur between Solfach 
and St. David’s. Among the more remarkable changes effected by 
the intrusive trap, he adverts to jaspidified schists inclosed between a 
large bifurcated mass of trap proceeding from Trafgarn. Having traced 
the Silurian system in a course of 120 miles from the Wrekin to Caer- 
marthen in ridges more or less parallel running from N.E.to S.W., the 
author has shown in former memoirs that this strike of the strata uni- 
formly coincides with the direction of linear outbursts of volcanic mat- 
ter. In Caermarthenshire vast dislocations and transverse breaks are 
exhibited by which the strata are for short distances thrown into 
E. and W. directions, but on the whole the south-westerly course is 
maintained. A ridge of intrusive rocks recently discovered, ranging 
between the rivers Towey and Taf (Castel, Cogan, &c.), having the 
same course, serves to explain how that dominant direction has been 
there preserved. In entering Southern Pembroke, however, the whole 
of the strata from the coal measures to the Cambrian rocks are thrown 
into an E, and W. direction, accompanied by violent contortions and 
powerful faults ; whilst in northern parts of the county the old N.E. 
and S.W. direction prevails. As these converging lines are accom- 
panied by linear, parallel ridges of trap rock, the author is confirmed in 
his belief that the forces which evolved the latter have been the proxi- 
mate cause of such directions; and he further refers the extraordinary 
convulsions and dismemberments to which the strata in Pembroke 
have been subjected, to the interference of two great lines of ele- 
vation dependent upon volcanic activity. In accordance with phe- 
nomena observed in other parts of S. Wales, it is remarked that all 
the superficial detritus is of local origin, the southern or lower part 
of the county being partially strewed over with the debris of the rocks 
which rise into mountains on the north coast. After some observa- 
tions on the blown sands, and the period of their formation, the author 
recapitulates the value of the Pembrokeshire coast sections in exhi- 
biting the “ Silurian System” precisely in the same geological position 
assigned to it from examinations in the interior ; and concludes by 
stating it as his opinion, that as this one county is shown to contain 
rocks in the true coal measures and in the old red sandstone, as well 
