258 Geological Society. 



veral places on this plain, and in some of the valleys are saline rivu- 

 lets and deposits of salt. 



The author afterwards offers some remarks upon the inhabitants, 

 and on the meteorological phenomena which he observed in the 

 neighbourhood of Bokhara; and concludes his memoir with a de- 

 scription of the sandy desert of the Turcomans, between the Oxus 

 and the Caspian Sea. 



Jan. 8, 1834. — A paper was read by Roderick Impey Murehison, 

 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 presented as the first of a series of communica- 

 tions 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 peculiar 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 

 the country described, such 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 argillaceous red marls of which it 

 consists, contain many beds of concretionary limestone or cornstone, 

 with some strata of sandstone. 



Remains of Crustacea have been found in this group, together with 

 defences of fish, S:c. 



c. The tile-stones are best exhibited in a remarkably rectilinear es- 

 carpment, extending from the north-western extremity of the Mvnidd 

 Eppint to near the mouth of the Towey, a distance of about thirty- 

 five miles. 



These beds contain fossils in Caermarthenshire, and also in their 

 north-eastern prolongation into Shropshire : among them are Lingula, 

 Avicula, three or four species of univalves,asmall species of Orthocera- 



