474 



thin and conglomeritic bands of the rock. Alternations: of red and 

 green marls again succeed beneath the cornstones, and the base of 

 the whole formation is usually marked, particularly in its course 

 from Kington to Caermarthenshire, by highly micaceous greenish 

 and reddish tile stones associated with marl. Thick-bedded, fine- 

 grained building stones of excellent quality are worked near Hay in 

 Herefordshire, overlying the tile stone division. No workable seam 

 of coal has ever been discovered in the old red sandstone. Dr. Lloyd 

 has recently discovered near Leominster and Ludlow, in the central 

 and calcareous sandstone beds of the formation, fossils which are 

 chiefly referable to undescribed species of the family of Trilobites, 

 and with them a few fragments of plants apparently terrestrial. 



An expansion upon a large scale is pointed out in the old red sand- 

 stone, which, from a narrow tongue, is described as extending all 

 over the forest of Mynidd Eppint, on the western side of which it 

 reposes conformably and at high angles, upon the uppermost strata 

 of grauwacke, at the chief escarpment of that rock. Many trans- 

 verse sections from the grauwacke formations to the edge of the Gla- 

 morganshire coal-basin are given by the author, and they exhibit a 

 perfect conformability between the upper beds of the old red and the 

 lower members of the mountain limestone, as well as a gradual pas- 

 sage from the old red into the grauwacke. He, however, insists 

 that there are no two formations of the English series which can be 

 better separated from each other for purposes of geological illustra- 

 tion, than the old red sandstone and the uppermost grauwacke; the 

 former being as poor as the latter is rich in organic remains, whilst 

 the colours and mineral characters of the two formations are also 

 very distinct. The maximum thickness of the formation is not easily 

 defined with accuracy, but the author has no hesitation in saying 

 that it exceeds 4000 feet. 



In the latitudes of Llandovery and Llandilo, the whole formation 

 is thrown so much on edge, that it necessarily occupies a very small 

 superficial breadth, whilst the very slight inclination and the undu- 

 lation of the beds in Herefordshire and Brecknockshire account for 

 its vast expansion in these counties. 



Detached tracts covered with this formation are pointed out as 

 occurring far within the frontier of the grauwacke rocks ; and they 

 are considered to be true basins of elevation which have been formed 

 on the western sides of certain anticlinal lines, along which the in- 

 ferior sediments have a reversed dip. 



April 17th. — Thomas Colbeck, Esq., Maddox-street, Regent- 

 street, was elected a Fellow of this Society. 



The second part of a memoir, commenced on the 27th of March, 

 and entitled, " On the sedimentary deposits which occupy the west- 

 ern parts of Shropshire and Herefordshire, and are prolonged from 

 N.E. to S.W., through Radnorshire, Brecknockshire, and Caermar- 

 thenshire, with descriptions of the accompanying rocks of intrusive 

 or igneous characters," by Roderick Impey Murchison, Esq. F.G.S. 

 F.R.S. &c, was read. 



In this part of the memoir the author separates into distinct for-, 



