Mr Poulett Scrope's Considerations on Volcanos. 855 



elevated, solely by the developement of subterranean expansion beneath, 

 and those secondary ranges, or axes of elevation, which consist in the con- 

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

 talline mass beneath these secondary convexities, were occasioned 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 causes productive of local variations in the resistance opposed 

 to the lateral movement of the strata, would occasion proportionate aber- 

 rations from this parallelism. The intervals between these parallel ranges, 

 that is the concave flexures, or fractures, produced the longitudinal val- 

 lies of mountain districts. In the north of Scotland, such vallies, sepa- 

 rated by intervening secondary ridges, are numerous and remarkable, 

 forming the basins of the greater number of her lakes and eestuaries. The 

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

 Alps, and that of Lombardy on the other, to be examples of longitudinal 

 vallies having this origin. The range of Jura on one side, and that of 

 the Apennines on the other, are in this view, the secondary ridges occa- 

 sioned by the replication in the strata, which were driven laterally to- 

 wards 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 transverse to the axis of eleva- 

 tion, by local irregularities in the mode or time of elevation. Many of 

 the transverse vallies of mountain chains are referred to this origin, par- 

 ticularly 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 

 retreating from the surfaces, thus suddenly raised above 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. (Diluvium of Switzerland, Piemont, the Italian lakes, 

 &c.) Other transverse vallies were, perhaps, wholly scooped out by 

 these retreating 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 ramifications, entirely excavated, 

 by causes still in action, more especially the fall of water from the sky, 

 and the erosive force of its descent from higher to lower levels. It is re- 

 marked, that there are good reasons for concluding that the quantity of 

 water circulating over the globe's surface in this manner, in given times, 

 has progressively diminished, with its diminution of temperature, from thi 



