Volcanos. 137 



this axis. Whatever expansions took place in the inferior crys- 

 talline mass beneath these secondary convexities, were occa- 

 sioned by the reduction of pressure on it, not by the absolute 

 increase of its expansive force, as in the primary axis. These 

 secondary ridges are more or less parallel to the primary. The 

 occurrence of proximate ranges of elevation, or any other cau- 

 ses productive of local variations in the resistance opposed to 

 the lateral movements of the strata, would occasion proportion- 

 ate aberrations from this parallelism. The intervals between 

 these parallel ranges, that is the concave flexures, or fractures, 

 produced the longitudinal vallies of mountain districts. In the 

 north of Scotland, such vallies, separated by intervening sec- 

 ondary ridges, are numerous and remarkable, forming the basins 

 of the greater number of her lakes and actuaries. The author 

 supposes even the great valley of Switzerland, on one side of 

 the Alps, and that of Lombarcly on the other, to be examples of 

 longitudinal valleys having this origin. The range of Jura 

 on one side, and that of the Appenines on the other, are in this 

 view, the secondary ridges occasioned by the replication in the 

 strata, which were driven laterally towards the north and south 

 by the forcible elevation of the primary range of the Alps. 

 In England the flcetz strata are supposed, by the author, to have 

 slid in a lateral direction towards the German ocean from off the 

 elevated range of Devon, Wales, Cumberland, and Scotland. 



" But besides the longitudinal fractures of the superficial strata, 

 others will often have been formed in a direction Irarisverse to 

 the axis of elevation, by local irregularities in the mode or 

 time of elevation. Many of the transverse vallies of mountain 

 chains are referred to this origin, particularly those deep chasm 

 like gorges which contain lakes at the foot of the higher Alps, 

 both on the north and south. The waters of the ocean retreat- 

 ing from the surfaces, thus suddenly raised abo e their level, 

 would retire with immense impetuosity through these fissures, 

 and enlarge and deepen them, leaving vast accumulations of 

 transported fragments at the lower extremity of such gorges, 

 where the velocity of the debacle was first checked. (Diluvi- 

 um of Switzerland, Piedmont, the Italian lakes, &,c.) Other 

 transverse vallies were, perhaps, wholly scooped out by these re- 

 treating waters, which would excavate their channels along those 

 lines into which they were directed by the accidents of level, and 

 the greater or less resistance of the rocks over which they rushed. 

 These vallies, according to the author, have been enlarged 

 and modified, and many others, particularly all the smaller rami- 

 fications, entirely excavated, by causes still in action, more es- 

 pecially the fall of water from the sky, and the erosive force of 

 its descent from higher to lower levels. It is remarked, that 



Vol. XIIL— No. 1. 18 



