PROCEEDINGS 



OF 



THE GEOLOGICAL SOCIETY OF LONDON. 



YoL. II. 1833—1834. No. 34-. 



Jan. 8, 1834. — George C. Lewis, Esq., of Henrietta Street, Lon- 

 don ; Thomas Jameson Torrie, Esq., of Edinburgh ; Peter B. Brodie, 

 jun., Esq., of Lincoln's Inn Fields ; Wm. Copland, Esq., of Edin- 

 burgh ; and Benjamin H. Bright, Esq., of Stone Buildings, Lincoln's 

 Inn, were elected Fellows of this Society. 



A paper was read by Roderick Impey Murchison, Esq., F.R.S., 

 F.G.S., " On the Old Red Sandstone in the Counties of Hereford, 

 Brecknock and Caermarthen, with collateral Observations on the 

 Dislocations which affect the north-west margin of the South Welsh 

 Coal-basin." 



This memoir is the first of a series of communications resulting 

 from researches made during the last summer. 



A short sketch is given of the structure of that portion of the car- 

 boniferous limestone of the South Welsh coal-field, which, in Breck- 

 nock andCaermarthenshires, is contiguous to those older formations, 

 which were the particular subject of the author's examination. 



After noticing some features which are common to the mountain 

 limestone in other districts, such as an oolitic structure, and the ex- 

 istence of caverns and funnel-shaped cavities, attention is specially 

 called to a portion of the limestone near Gwinfe in Caermarthenshire, 

 the exterior of which exhibits a high polish. .As these polished beds 

 protrude from the edge of a turf bog, it is suggested that such effects 

 may have been produced by the long-continued action of a weak ve- 

 getable acid issuing from the morass, and altering the surface of the 

 rock. 



I. Old Red Sandstone. — The old red sandstone is divided into 

 three groups. 



a. Conglomerate and sandstone, b. Cornstones and marl. c. Tile- 

 stones. 



a. The uppermost of these groups, occupying the loftiest summits 

 of the country described, as the Brecon and Caermarthen Fans, is 

 uniformly capped by a band of conglomerate, underlaid by a vast 

 thickness of sandstone. Neither calcareous beds nor organic remains 

 have been discovered in this group. 



b. The central group is spread in undulating masses over the 

 greater part of Herefordshire. The red argillaceous marls of which it 

 consists, contain many beds of concretionary limestone or cornstone, 

 with some strata of sandstone. 



Vol. II. 



