198 



(new) red sandstone series skirls^ they are generally separated from 

 the grauwacke by conglomerates, or sandstones, which do not contain 

 the detrital remains of trappean rocks. Hence the author considers 

 that the (new) red sandstone series of the district generally was, to a 

 certain extent, in the course of formation when the volcanos came into 

 activity, 



A description is given, accompanied by a section, of the manner in 

 which the trappean rocks of Washfield, near Tiverton, are associated 

 with the (new) red sandstone of the same locality, and it is inferred 

 from the facts detailed, that events there succeeded each other in the 

 following order : 1 . An original subaqueous valley or depression in 

 the grauwacke. 2. A deposit of detrital matter derived from the 

 subjacent grauwacke. 3. An eruption of igneous substances, in the 

 manner of modern volcanos, beneath very moderate pressure. 4. The 

 deposit of detrital matter, in a great measure derived from the neigh- 

 bouring grauwacke, mingled with fragments of trappean rocks, many 

 of which may have been ejected, as fragments now frequently are, 

 from volcanic craters. 5. Denudations at various geological epochs 

 since the period of the (new) red sandstone, which have left the 

 rocks as we now find them. 



It is noticed as a fact, which the author conceives to be of difficult 

 explanation without the aid of this volcanic hypothesis, that in the 

 localities where the trappean rocks, associated with the red sandstone, 

 occur, there are numerous angular fragments, some of considerable 

 magnitude, even equal to one or two tons in weight, intermingled 

 with the conglomerates, which do not resemble any trappean rocks 

 discovered, in place, within the district. These fragments principally 

 consist of reddish brown quartziferous porphyry, the base being fel- 

 spathic, and the contained crystals being those of quartz and glassy 

 felspar, the latter often attaining a large size. Though quartziferous 

 porphyry is pbservable in place in some situations, as, for instance, 

 to the northward of Dunchideock, near Exeter, it does not contain 

 the large crystals observable in numerous fragments of porphyry in- 

 cluded in the red conglomerates. The author, therefore, is inclined 

 to consider, that these angular fragments have been ejected from vol- 

 canic vents, and that, falling upon the detrital matter then in the course 

 of deposition around such vents, they became included among it. Tt 

 is remarked that these fragments, as well as those of the more com- 

 mon, scoriaceous, and other trappean rocks, found in place, do not 

 form component parts of the red conglomerates beyond somewhat 

 moderate distances, measured from situations where the existence of 

 volcanic vents, during the early part of the (new) red sandstone epoch, 

 may be considered a probable inference, from the various, observed 

 phsenomena. 



A memoir was next read " On the range of the Carboniferous Lime- 

 stone flanking the primary Cumbrian Mountains ; and on the Coal- 

 fields of the N.W. Coast of Cumberland, &c. ;" by the Rev. Adam 

 Sedgwick, F.G.S., Woodwardian Professor in the University of Cam- 

 bridge, and Williamson Peile, Esq., F.G.S., of Whitehaven. 



