4J4 Theories of the Formation of Mountains* 



tances in certain directions, may all be results of the same kind 

 of action. It also accords well with established facts to assume 

 that the solid crust overlying a region where the subterranean 

 heat is increasing in intensity, becomes gradually upheaved, frac- 

 tured, and distended, the lower part of the newly opened fissures 

 becoming filled with fused matter, which soon consolidates and 

 crystallizes. These uplifting movements may be propagated along 

 narrow belts, placed side by side, and may have been in progress 

 simultaneously, or in succession, in one narrow zone after another. 

 " When the expansive force has been locally in operation for a 

 long period, in a given district, there is a tendency in the subter- 

 ranean heat to diminish ; — the volcanic energy is spent, and its 

 position is transferred to some new region. Subsidence then 

 begins, in consequence of the cooling and shrinking of subterra- 

 nean seas of lava and gaseous matter : and the solid strata col- 

 lapse in obedience to gravity. If this contraction take place along 

 narrow and parallel zones of country, the incumbent flexible strata 

 would be forced, in proportion as they were let down, to pack 

 themselves into a smaller space, as they conformed to the circum- 

 ference of a smaller arc. The manner in which undulations may 

 be gradually produced in pliant strata by subsidence is illustrated 

 on a small scale by the creeps in coal-mines ; there both the over- 

 lying and underlying shales and clays sink down from the ceihng, 

 or rise up from the floor, and fill the galleries which have been 

 left vacant by the abstraction of the fuel. In like manner the 

 failure of support arising from subterranean causes may enable the 

 force of gravity, though originally exerted vertically, to bend and 

 squeeze the rocks as if they had been subjected to lateral pres- 

 sure. 



" Earthquakes have raised to heaven the humble vale, 

 And gulphs the mountain's mighty mass entomb'd, 

 And where th' Atlantic rolls, wide continents have bloom'd." 



"In applying these lines to the physical revolutions of the terri- 

 tory at present under consideration, we must remember that 

 the continent which bloomed to the eastward, or where the 

 Atlantic now rolls its waves was anterior to the origin of the 

 carboniferous strata which were derived from its ruins ; whereas 

 the elevation and subsidence supposed to have given rise to the 

 Appalachian ridges was subsequent to the deposition of the coal- 

 measures. But all these great movements of oscillat'on were 



