352 Analysis of Scientific Books and Memoirs. 



formable to observation from a variety of instances, the existence of active 

 volcanos obviates the occurrence of such extensive elevations of the su- 

 perficial strata, by letting off, through fissures in these strata, the super- 

 fluous caloric which would otherwise accumulate and produce succes- 

 sive powerful expansions of, in the great bed of lava beneath them, we 

 must expect to find such spiracles to be frequent in the lower levels of 

 the globe's surface, and rare in those higher, — and this is precisely true 

 to the letter; for we know of very few volcanic vents in the interior of the 

 continents, or amongst mountain ranges, while they rise in vast numbers 

 from the depths of the ocean. If the Andes are urged as a striking ex- 

 ception, it is replied, that this great range is itself composed almost wholly 

 of volcanic, or, at least, pyrogenous rocks, which, like iEtna, Teneriffe, 

 &c. have swelled to their immense height by the accumulated ejections 

 of very productive vents. 



But, notwithstanding the distance usually interposed between the prin- 

 cipal trains of volcanic vents, and the elevated continental ranges, Mr 

 Scrope thinks he perceives a frequent and remarkable parallelism in their 

 direction. Thus, the volcanic trains of France, Germany, and Italy, run 

 decidedly parallel to the opposite ranges of the Alps and Apennines ; 

 that immense chain which encircles the Pacific, is almost uniformly pa- 

 rallel to the neighbouring high lands of Asia and America, &c. ; and he 

 is thus led to suppose, that the creation of fissures of elevation, and the 

 protrusion through them, of crystalline rock, chiefly in a more or less so- 

 lid state, together with the heaving, dislocation, and contortion of the 

 strata on either side the cleft, that process, in short, to which he attri- 

 butes the production of mountain ranges, was the immediate and primary 

 result of partial expansions of the subterranean lava-bed at a great 

 depth ; while the fissures of eruption, which give rise to the properly so 

 called volcanic eruptions, on different points of these cracks, were second- 

 ary and incidental results of this process, being chiefly occasioned by the 

 lateral drag of the superficial strata towards the line of elevation, which 

 the action of a powerful force, heaving them upwards on this line, must 

 necessarily produce. The author remarks, that the generalization of this 

 important fact, that the elevation, en masse, of the solid strata, composing 

 the crust of the earth, has been inversely proportional to the develope- 

 ment of the volcanic phenomena in the same quarter of the globe, demon- 

 strates, that the subterranean bed of intensely heated crystalline rock, 

 (or lava,) whose local existence was proved in the early part of his essay, 

 must extend generally beneath the whole surface of the globe. The 

 transmission of caloric to this bed, from within, appears also to have been 

 uniform and constant, having produced successive expansions in it, and 

 proportional elevations of the overlying surfaces in those parts where no 

 facilties existed for the outward escape of the caloric, and continual erup- 

 tions attended with little or no elevation, wherever vents were created for 

 the extravasation of the heated and intumescent matter. 



In the Xth Chapter, " on the Developement of Subterranean Expan- 

 sion in the elevation of strata, and production of continents above the sur- 



11 



