226 



The remainder of the fossils was obtained by Dr. Potts at the 

 western entrance of Bodmin^ and by Mr. De la Beche from the vi- 

 cinity of Liskeard, on a prolongation of the same strata. 



Altered or metamorphic rocks, having frequently the appearance of 

 gneiss, mica slate, hornblende rock_, &c., occur in the neighbourhood 

 of Tintagel and Camelford ; and Mr. De la Beche says, that a little care 

 in tracing these rocks shows that they are altered portions of strata 

 which possess the usual and varied characters of grauwacke. In con- 

 clusion he observes, that there is every reason to believe that two 

 movements have taken place of the land in Somerset, Devon, and Corn- 

 wall, one to a height of 30 or 40 feet above the present sea-level, and 

 another to an uncertain depth beneath it, since the vegetation of the 

 land and the molluscous inhabitants of the neighbouring sea were the 

 same as they now are. 



January 20, 1836.— Arthur William Tooke, Esq., A.M., of Rus- 

 sell-square; J. Jukes, Esq., B.A., St. John's College, Cambridge 3 

 Richard Zacchary Mudge, Esq., F.R.S., Capt.in the Royal Engineers, 

 Highwood Hill, Middlesex ; and Philip Worsley, Esq., of Great Or- 

 mond-street, were elected Fellows of the Society. 



A paper was read " On the geological structure of Pembrokeshire, 

 more particularly on the e.xtension of the Silurian system of rocks 

 into the coast cliffs of that county." Bv Roderick Impey Murchison, 

 Esq., V.P.G.S. 



This memoir was prefaced by an account of the origin of the terms 

 Silurian and Cambrian Systems as applied to the older sedimentary 

 deposits. Having occupied several years in establishing a fixed order 

 of succession amid the strata of age anterior to the old red sandstone, 

 and having finally named the formations in descending order, the 

 Ludlow rock, Wenlock limestone, Cai'adoc sandstones, and Llandeilo 

 jSags, the author was urged by many leading geologists to propose a 

 new, comprehensive name for this group, and thereby to prevent the 

 confusion which had so long prevailed by the use of the words" Trans- 

 ition" and " Grauwacke." He adopted the term Silurian System, be- 

 cause the territory in which the successive formations above mentioned 

 are exhibited, was formerly occupied by the ancient, British people the 

 Silures. The Silurian rocks are underlaid by vast masses which rise 

 up into the mountains of North, and the western part of South Wales, 

 and to these Professor Sedgwick, connecting his labours with those 

 of Mr. Murchison, has assigned the name of " Cambrian System." 

 A portion of last summer was employed in tracing these rocks from 

 Caermarthenshire into Pembroke, and in doing this the author was 

 led to attempt a general survey of the county, examining the strata 

 from the youngest to the oldest, dwelling, however, specially on the 

 deposits of the " Silurian System." 



Owing to its peninsulated form and the transverse fissures proceed- 

 ing from Milford Haven into the heart of the county, Pembrokeshire 

 affords great facilities for the comprehension of its mineral structure, 

 and as the chief masses range from E. to W., sections from S. to N. 



