age or Arthur's seat, Edinburgh. 145 



detect traces in studying the great series of rocks on the north side 

 of the Hunter's Bog ; and to them must probably be primarily 

 ascribed the remarkable preservation of the fragments of this old 

 volcano as its rocks gradually sank below the sea-level, and were 

 buried under the newer Carboniferous deposits. 



Fourth. That grand series of movements to which, in long subse- 

 quent times, the whole of the rocks of the district were subjected, 

 and in consequence of which they were bent into those great folds 

 of which we everywhere see such striking evidence. 



The fragments both of the subaerial and subterranean portions 

 of this old volcano which have escaped destruction have been 

 determined entirely by their position and durability. The rocks 

 formed at the surface have been subjected to two periods of denuda- 

 tion, that which elapsed between their formation and their being 

 buried in younger deposits, and that which supervened when the 

 latter were stripped away after the rocks had been brought into 

 something like their present positions by subterranean movements. 

 The subterranean intrusions have suffered only during the later period 

 of denudation. All the southern portions of the products of this 

 igneous vent, with the surrounding strata, have been entirely swept 

 away, in consequence of their great elevation towards the crown of 

 the anticlinial ; consequently in the great scar along which the 

 Queen's Drive is cut, we are enabled to study the contents of the 

 great fissure. Along the northern portions of the group of hills, 

 all the ridges are capped with masses of lava of exceptional hard- 

 ness and durability. 



The history of the formation of Arthur's Seat, briefly summarized, 

 would appear to have been as follows : — 



At about the middle of the Calciferous-Sandstone period (Lower 

 Carboniferous) a great fissure opened in the district, began to emit 

 at several points along its course discharges of vapour carrying with 

 them fragments of rock, cinders and ashes, alternating with the 

 outflow of currents of lava. The liquefied products appear to have 

 been both of the basaltic and the trachytic class, or sometimes of 

 that intermediate variety called by Abich " Trachy-dolerite." As 

 in some existing volcanoes, these different products do not appear 

 to have been ejected in any definite order ; but periods during which 

 basalts were ejected alternated with others, during which more sili- 

 ceous lavas were poured forth. 



At the same time, probably, with these ejections at the surface, 

 masses of the more liquid materials of the basaltic class found their 

 way along planes of weakness in the surrounding strata, and, instead 

 of being forced out at the surface, consolidated in great subterranean 

 intrusive sheets. Owing to the extensive denudation on the south 

 side of the hill, the connexion of two of these injected masses, 

 those of St. Leonard's and Salisbury Craigs, with the consolidated 

 vertical duct of lava known as Samson's Ribs can still be traced. 



That the earlier eruptions of this locality took place in shallow 

 water appears certain, from the nature of the fossils found in the 

 stratified tuffs at St. Anthony's Chapel. Of the exact site of the 



