1 36 Volcanos. 



schistose rocks, whose parallel plates of mica are enabled to slip, 

 with more or less facility, over one another ; such rocks appear 

 to have often suffered an extraordinary degree of replication. 

 By the subsequent destruction of the extreme flexures of these 

 folded strata, they seem, to a traveller passing across their edges, 

 to alternate repeatedly in a recurring series. Where the indu- 

 ration was more complete, or the structure of the rock unfa- 

 vourable to flexibility, as in the compact and massive lime- 

 stone formations, numerous fractures, fissures of all sizes, often 

 of great width, Tviit have been broken through them, and the 

 intervening masses of strata more or less dislocated and dis- 

 turbed in their position, sometimes, perhaps, left in isolated 

 patches on summits or flanks of the protruded crystalline rocks. 

 This appears to have been the origin of the insulated pyra- 

 mids of dolomite, which rise from the great porphyry district 

 of the Tyrol. Indeed, any one acquainted with the aspect of the 

 limestone formations of the whole range of the Alps, will ac- 

 knowledge, that, in this irregularity of position and inclination, 

 their perpendicular escarpments, and chasm-like vailies, these 

 vast masses of strata accord precisely with what might be expect- 

 ed from a mode of elevation, such as is here attributed to them. 

 Thus, of the fissures broken through the elevated strata, those 

 which descended sufficiently in depth, and opened into the inferior 

 lava-bed, occasioned extravasations of this substance, producing 

 dikes, &c. others which were too narrow and intricate to allow 

 of their occupation by the intumescent matter, were yet perme- 

 able to the vapors that rose from this subjacent and intensely 

 heated mass, bringing with them both earthy and metallic sub- 

 limations, which would be deposited on the sides of the fissures, 

 together with fragments broken from these sides, or fallen from 

 their upper parts, whence the mineral veins. Those fissures 

 which did not communicate with the heated lava-bed, were fil- 

 led in part, or altogether, by rubbish alone, and these are the 

 faults or slips of miners. The formation of calcareous and other 

 breccias and veined-marbles, is accounted for by the smallest of 

 these fractures ; the still unconsolidated juices of the rock oozing 

 into its cracks and crevices, and filling them with a deposit of 

 finer matter. The quartz veins of the arenaceous and micaceous 

 rocks are attributed to the same process. 



" The author goes on to draw a distinction between the prima- 

 ry range, or axis of elevation, along which the overlying strata 

 were burst open and elevated, solely by the developement of sub- 

 terranean expansion beneath, and those secondary ranges, or 

 axes of elevation, which consist in the convex flexures produced 

 on either side of, and more or less distant from, the primary axis, 

 by the replication of the elevated strata, as they slipped away from 



