878 



THE WONDERS OF GEOLOGY. Lect VIII. 



that prodigious masses of granite and other hypogene rock^, 

 have been raised into ridges and mountain-chains, at various 

 periods, and long after their first formation and subsequent 

 consolidation. In many cases the protrusions are local 

 and of comparatively small extent, at least so far as their 

 distribution on the surface is concerned ; for very distant 

 isolated peaks of plutonic matter may have a deep-seated 

 connexion. But in other instances the elevatory force has 

 embraced a vast area, and entire mountain-chains have been 

 simultaneously and permanently lifted up, and now remain 

 in parallel ranges ; the subordinate parts of any one period 

 or system of elevation, being in accordance as to position 

 and direction with the principal upheaved masses. Admit- 

 ting the general correctness of these views, it follows that 

 mountain-ridges composed of vertical or highly inclined 

 beds, emerging from beneath horizontal deposits, must 

 have been thrown up subsequently to the deposition of the 

 latter ; and that their upheaval was succeeded by a long 

 period of repose, during which the flanks of the moun- 

 tains beneath the sea were covered by the horizontal sedi- 

 ments ; the latter, elevated above the waters, by subsequent 

 movements, now form the fertile plains which surround the 

 base of the Alpine districts. 



Professor Sedgwick remarks, that if we admit that 

 the higher regions of the globe have been raised from 

 the sea by any modification of volcanic force, we must 

 also admit that there have been many successive epochs 

 of extraordinary plutonic energy, separated from each 

 other by long periods of repose.* The sudden forma- 

 tion of mountain -peaks by violent upbursts of sub- 

 terranean force, may be regarded as paroxysmal efforts 

 of the expansive power, by whose long-continued and 

 imperceptible action the elevatiqn of continents, and of 



* Anniversary Address to the Geological Society, for 1831. 



