Geological Society. 515 



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

 manner of modern volcanoes, 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 observable 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. It 

 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 

 phenomena*. 



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

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



* [The geological reader may eompare, perhaps with some advantage, 

 the inferences stated by Mr. De la Beche in the very interesting memoir 

 noticed above, with a paper on the consolidation of the new-red-sandstone, 

 published in the Phil. Mag. and Annals, N. S., vol.vi. p. 71— 75. The 

 views offered in that paper were suggested to me, in part, by certain phe- 

 nomena of the association of trappean rocks with the new-red-sandstone 

 in Devonshire, as exhibited principally at Kellerton and Thorverton (and 

 many of which are now described by Mr. De la Beche,) and by analogous 

 cases in the rothe todte liegende of the Continent of Europe, as described 

 by various foreign geologists. An error which I committed on another 

 subject, connected indirectly with this, and mentioned in an accompany- 

 ing notice (Phil. Mag. and Annals, N. S., vol. vi. p. 75 — 76), was cor- 

 rected by Mr. Featherstonhaugh, in the succeeding volume (vii. p. 198 — 

 201); but the remark of that geologist, that "any desiccated salt lake" 

 might be expected to contain the peculiar aggregates of crystals of chloride 

 of sodium, the production of which I had ascribed to the agency of heat, 



