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the (new) red sandstone series of Somersetshire and the more north- 

 ern portions of Devonshire: the southern portions of the latter county 

 afford many excamples of the association of trappean rocks with the 

 lower parts of this series, particularly near Tiverton^ Thorverton, Sil- 

 verton, Kellerton Park, Crediton, and Exeter. 



When hastily viewed, the trappean rocks might be mistaken for 

 masses of igneous matter which have been intruded, in a state of fu- 

 sion, among the beds of red sandstone. A more detailed examination 

 of the various facts connected with their mode of occurrence leads, 

 however, in the opinion of the author, to the inference that they have 

 been produced by volcanic action during the formation of the lower 

 parts of the (new) red sandstone series ; in fact, that the trappean rocks 

 in question are the remains of melted rock, either ejected from, or re- 

 tained within the pipes of, volcanos which were in a state of activity 

 during the production of the lower part of the (new) red sandstone 

 series of Devonshire. 



The author endeavours, in the first place, to point out the relative 

 geological age of the red sandstones and conglomerates with which 

 these trappean rocks are associated in Southern Devon, by showing, 

 that in their continuation to the northward, along the skirts of the 

 grauwacke to the shores of the Bristol Channel, they pass into a series 

 of beds which is crowned by magnesian limestone and conglomerate, 

 equivalent to the magnesian limestone and conglomerate of the Men- 

 dip Hills and the vicinity of Bristol. The beds beneath the magnesian 

 conglomerate, which very rarely passes into a magnesian limestone, 

 from the absence of pebbles derived from older rocks, consist, for the 

 most part, of red or claret-coloured sandstones, with an occasional 

 seam or bed of conglomerate, the cementing matter of which is not 

 calcareo-magnesian. Their thickness is necessarily variable, from the 

 uneven surface of grauwacke, upon which the sandstones rest uncon- 

 formably ; but it amounts to about one hundred and fifty feet in the 

 vicinity of Wiveliscombe. The author points out, by the aid of sec- 

 tions, that the magnesian conglomerate may readily rest upon the 

 grauwacke, and conceal the lower red sandstone series by over- 

 lapping it, and that therefore it becomes exceedingly difficult to ob- 

 tain an average thickness of these lower red sandstones, which, if 

 we consider the magnesian conglomerates of the Mendip Hills as an 

 equivalent of tlie zechstein of Germany, would be equivalent to the 

 rathe todte liegende of the same part of Europe, and therefore be of 

 the same geological age as the lower red sandstones of the North of 

 England described by Prof. Sedgwick, and the beds noticed by Mr. 

 Murchison. 



Having thus obtained the relative geological age of the beds 

 with which the trappean rocks are associated, the author proceeds 

 to point out the occurrence of beds of sand among the more common 

 red sandstone, which presents every appearance of having been vol- 

 canic sands ejected from a crater, and which became subsequently 

 mixed with common detrital matter then depositing. It is stated that 

 though the trappean rocks may sometimes be seen, as in the vicinity 

 of Exeter, to rest as if they had overflowed the grauwacke which the 



