96 REPORT— 1869. 



2. Tliat the last time tliese plains ^N-crc exposed to tbc levelliug action of the 

 sea was probably duriug the Upper (;■') Miocene period. 



.3. That the rivers of this district are identical, at least iu their higher regions, 

 ■with those which flowed formerly from tlie central diy land into the Miocene sea. 



4. That the valleys at the bottom of which these rivers run are the result of 

 their own erosive action, aided bj' other subaerial agents. 



.5. That the uniformity of width and depth of these vallej's is due to the degree 

 of hardness of the rocks in this country, being in an order of succession exactly 

 corresponding to the time during which they have been exposed to the action 

 of subaerial denudation. 



Notes on some Oranites of Loiuer Brittany. By G. A. Leboijr, F.R.G.S. 



This paper is an attempt to determine, as far as possible, the relative ages of the 

 granites of Lower Brittany, and various sections are given, illustrating their appa- 

 rent bedding in the westernmost part of the province. 



The author believes the granite to the north of Cleden to be metamorphic. 



On the Distribution of the British Fossil LatnellihrancJiiata, 

 By James Logan Lobley, F.G.S. 



This paper gave the results of an investigation into the distribution of the fossil 

 Lamellibranchiata found in British strata ; and was accompanied by a series of 

 diagrammatic tables showing the details of the distribution, and bj' lists of the 

 species hitherto discovered in each formation. 



On the Gold of Natal By R. J. Mann, M.D., F.B.A.S. 



On the Traitpean Conglomerates of Middletown Hill, Montgomeryshire. 

 By G. Maw, F.G.S., F.L.S., F.S.A. 

 This was a description of the contemporaneous traps of Lower Silurian age ia 

 the ridge known as Middletown Hill, running parallel with the Breiddens, on the 

 borders of Shropshire and Montgomeryshire. Especial refei-ence was made to the 

 great beds of bouldered trap, consisting of boulders of compact felstone imbedded 

 in a softer matrix of felspathic tuti" The nodules occupy about half the mass of 

 the conglomerate, and are unaccompanied by pebbles of any other rock. They 

 vary from the size of a walnut to rounded masses of more than a hundredweight. 

 Sir R. Murchison's description of these beds was referred to, and the author took 

 exception to the term "concretionary trap " employed in the ' Silurian Sy.stem,'as 

 he considered that the rounded outline of the boulders was unquestionably due 

 to }nechanical causes. The interbedded traps, bounded on either side by Lower 

 Llandeilo Flags, are of a collective thickness of about 780 feet, including 

 bouldered felstone, alternating with a whitish-green felspathic breccia. The line 

 of separation between the breccia-bed and boulder-trap is remarkably sudden, and 

 no gradation of character occurs between them. The breccia is worked for hard 

 felspar used for pottery purposes, and contains small nests of steatite. The boul- 

 dered condition of the felstone-bed was considered due to its partial breaking 

 up on being erupted under water, the soft matrix of felspathic tutf being the por- 

 tion more intimately divided, and the compact boulders fragments that had re- 

 sisted disintegration. The sudden alternation in Middletown Hill of eruptive 

 beds of very dissimilar character was noticed ; they seem to have been emitted 

 in immediate succession, as, although overlain and underlain by sedimentary 

 deposits, there is no evidence of interstratification of sedimentary beds. The 

 author, in conclusion, pointed out the close geographical association with these 

 bedded traps of the much later porphyritic greenstone of the Breidden Hills, 

 which, it was suggested, might have been emitted from the same point of erup- 

 tion ; and the local association of the intrusive gi-eenstone with the Lower Silurian 

 interbedded felstones was noticed as being very general in North Wales. 



