230 



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 phae- 

 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 

 v/hich 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 

 as in the Silurian and Cambrian systems, which from their lithological 

 characters have been mistaken for " greywacke," the use of that word 

 as expressing the age of rocks is no longer consistent with the ad- 

 vanced state of geological science, and that if used, the name should 

 either be rigidly restricted to some of the very oldest sedimentary de- 

 posits, or simply employed as a mineralogical definition of peculiar grits 

 which actually reoccur in strata formed in many succesive epochs. 



Feb. 3. — James Thompson, Esq., F.R.S., of Primrose Hill near 

 Clitberoe ; James Winter Scott, Esq., M.P., of Rotherfield Park, Hants, 

 and Grafton-street J and George Warde Norman, Esq., of Bromley, 

 Kent, were elected Fellows of this Society. 



A paper on " The Gravel and Alluvia of S. Wales and Siluria as 

 distinguished from a northern drift covering Lancashire, Cheshire, 

 N. Salop, and parts of Worcester and Gloucester," by R. I. Murchi- 

 son, Esq.,V.P.G.S., was read. 



The first part of this memoir describes the detritus in the Welsh 

 and Silurian territories. The surface of this region is completely 

 exempt from the debris of any of those far-transported rocks which 



