218 THE CRUST AND INTERIOR OF THE EARTH. 



heated matter but cannot convert matter which is in a fluid or viscous 

 state from heat, into a sohd. It would retain the moving property of a 

 fluid so long as it retained its heat. 



If the behaviour of the internal mass of the earth during the process 

 of coohng was similar to that of lava or basalt, 



(1.) — -The solidification would commence at the surface. 

 (2.) — The matter in passing from the liquid or viscous to the sohd 

 state would attach itself to the parts already solid, i.e., to the 

 under suii'ace of the aheady sohd crust. 

 (3.) — The matter in becoming solid from loss of heat would for the 



most part contract. 

 (4.) — The process of coohng and sohdification would not take place 

 regularly, owing to the difference in temperature at which different 

 substances become solid, and the difference in the conductivity 

 of different parts of the crust overlying the heated matter. 

 (5.) — The solidified portion or the crust would press on the hquid 



or viscid interior until it became self -supporting. 



(6.) — Gravity would require the several parts of the crust to be in 



equihbiium. The disturbance of the equilibrium of the crust 



by irregularity in its growth would be restored by the action of 



gravity upon it. 



The elevation of continents and mountain chains, and the formation 



of deep oceanic areas and other synclinal depressions, are produced by 



the long continued action, in a particular direction, of lateral or 



horizontal pressure or compression resulting from the sinking of 



the crust on the contracting internal mass on which it rests. 



The eiiect of lateral pressuie is shown both by the minute 



plication of laminated strata, as in the cuttings through Lias clay 



of the new railway between Cheltenham and Banbury, or in 



the folding of a large expanse of surface as shown by Professor Dana 



to have been the way in which the Alleghany Mountains wore formed. 



The parallelism of mountain ranges, and of the outcrop or strike of 



strata in the same area, which results from the action of lateral pressure 



upon tbe crust in the same direction, is well illustrated in England. 



The change in the movement by which any area which has been 

 previously elevated undergoes depression, or vice versa, imphes a change in 

 the conditions by which the action of lateral pressure is directed. Such 

 changes are caused by irregularity in the gi-owth of the crust and the 

 consequent disturbance of its equilibrium. Such changes could not be 

 produced by the mere settlement of dead materials into a more compact 

 state. Such a process of consolidation would commence at the centre 

 and progress upwards, and when the interior had once become compact, 

 no undulation of the surface would be possible. With such a condition 

 of the interior the surface of the earth could not be changed. It would 

 be levelled by denudation, and the ocean would spread over the whole. 

 Tcn'cstrial life would cease to exist for want of a footing. A self- 

 supportiug crust would be equivalent to a solid earth. The undulatory 

 movement of the crust was greater in early geological periods than now. 

 ]the Cambrftin and Silurian strata comprise deposits of some six miles 



