362 Rev. D. Williams on Volcanic interferences with the 



so many focal residua of the several volcanic centres ; and 

 their universally-accompanying greenstones, trappsean ash, 

 schists, and slates, successive superfluous rejectamenta of 

 paroxysmal crater eruptions, or more regulated and constant 

 emanations from the many vomitories which now traverse the 

 ancient volcanic areas ; — it would appear obvious that the 

 several detached volcanic assemblages in different parallels, 

 having some given linear direction or range, would properly 

 pertain to remote local phases of ancient submarine volcanic 

 activity, and be remotely separated in age or time. The 

 abundantly -varied mineral components of such several assem- 

 blages, may therefore, I take it, be with more propriety termed, 

 generically, thermogenous products^ rather than " Plutonic, 

 pyrogenous, or metamorphic rocks ;" the two former terms 

 being commonly applied to the granites, porphyries, and green- 

 stones, and the latter (which is incalculably less capable of 

 being sustained, though propounded by the great Dr Hutton) 

 to their congenerous, cognate, and universally-associated 

 slates and schists. This is done under the notion that they 

 all pertain to one epoch, and are the results of some ima- 

 ginary phases of change which our planet has undergone, in 

 some process of condensation from a gaseous and fluid to an 

 incrusted condition. Or it may be supposed, that by some 

 alchemical transmutation, sandstones, limestones, and argil- 

 laceous rocks have been mysteriously converted into fossili- 

 ferous, carbonaceous, arenaceous, and crystalline slates. 



As a sequel, therefore, to the former Notices which I have 

 had the gratification to offer to the Geological Society of Corn- 

 wall, I wish briefly to state, that for some years past I have 

 satisfied myself that the old red sandstone of the British Isles 

 has been subjected to three protracted phases of volcanic in- 

 terference. 



The first, and most ancient of these systems, is seen in Scot- 

 land, where the granite, gneiss, and slate axis of the Gram- 

 pians, has been protruded through the older red, or the " pri- 

 mary red sandstone" of Mr MacCulloch. This, after a series of 

 intermittences, appears to have enfeebled down at about the 

 close of the Cambrian system, and ultimately to have expired 

 in the Silurian. The second system of protracted interfe- 



