224- Geological Society. 



enormous mass of matter deposited by this sea of mud, leaving only 

 detached portions as monuments of the passing of the mighty torrent. 



March 27. — The first part of a memoir "On the sedimentary de- 

 posits which occupy the western parts of Shropshire and Hereford- 

 shire, and are prolonged from N.E. to S.W., through Radnor, Breck- 

 nock, and Caermarthenshires, with descriptions of the accompanying 

 rocks of intrusive or igneous characters," by Roderick Impey Mur- 

 chison, Esq. F.G.S. F.R.S. &c, was read. 



After adverting to the want of definite knowledge of the order of 

 succession, and of the fossiliferous characters of those great deposits 

 anterior to the old red sandstone, and commonly called transition 

 rocks (fossiliferous grauwacke, De la Beche), the author states that 

 the task of attempting to separate them into distinct formations, was 

 first suggested to him by the very clear and perfect exhibition of their 

 details in the country under review. 



The present work has already occupied large portions of the two 

 last summers, and has for its basis the maps of the Ordnance survey, 

 coloured geologically by the author. To the Master General of the 

 Ordnance, to Col. Colby, Capt. Robe, and the Officers of His Majesty's 

 Map-office, for their assistance in supplying him with good geogra- 

 phical data, and also to Mr. Budgin, one of the Field-Surveyors of 

 the Ordnance, the author acknowledges his obligations. He next ad- 

 verts to the unpublished yet valuable observations of Mr. Arthur Aikin, 

 made many years ago in the north-eastern portion of the country de- 

 scribed ; and he further expresses his sincere thanks to many resident 

 gentlemen who assisted him in his observations. 



The memoir is divided into three parts. The first contains an ac- 

 count of the overlying deposits of new red sandstone, coal measures, 

 mountain limestone, and old red sandstone, each of which is in con- 

 tact with, or contiguous to, the transition rocks (grauwacke series) in 

 some portion of the region described. The second and most exten- 

 sive part explains the subdivisions and relations of the grauwacke se- 

 ries as exhibited within a zone of country extending from the Wrekin 

 near Shrewsbury on the N.E., to the mouth of the Towey, near Caer- 

 marthen, on the S.W. ; and the third part is to be devoted chiefly to 

 the consideration of the rocks of intrusive or igneous characters, and 

 their effects upon the associated strata. 



Part I. On the New Red Sandstone, Coal Measures, Mountain 

 Limestone, and Old Red Sandstone. 



1 . New red sandstone. — This is the youngest secondary formation 

 in contact with the transition rocks, and is exhibited on both sides of 

 the Severn, near Shrewsbury, being superposed to coal measures, to 

 various members of the grauwacke series, and to trap rocks of diffe- 

 rent characters, in all of which situations it is undisturbed. 



The oldest strata of this formation are compared with the rothe- 

 todte-liegende of Germany, or the older new red of the North of En- 

 gland, and are shown to underlie a dolomitic conglomerate at Alber- 

 bury and Cardeston. The superior members on the north bank of 

 the Severn, consist of fine-grained sandstones, for the most part red, 

 but offering at Grinshill, 7 miles N.E. of Shrewsbury, a subordinate, 



