the Earth's Contraction from Cooling. 373 



existence, through a large part of geological time, of a thin crust, 

 and of liquid rock beneath that crust so as to make its oscilla- 

 tion possible, and refers the chief oscillations, whether of eleva- 

 tion or of subsidence, to lateral pressure from the contraction 

 of that crust ; and this accords with my former view, and with 

 that earlier presented by the clear-sighted French geologist, 

 Prevost. 



I hold also, as before, that the prevailing position of moun- 

 tains on the borders of the continents, with the like location of 

 volcanoes and of the greater earthquakes, is due to the fact that 

 the oceanic areas were much the largest, and were the areas of 

 greatest subsidence under the continued general contraction of 

 the globe. 



Beyond these points there are additions and modifications. 

 In addition to admitting the nucleal solidity of the globe, and 

 the present partial union of the crust to the nucleus, these in- 

 clude the recognition of the following principles : — 



(1) That in mountain-making on the continental borders, the 

 oceanic crust had the advantage, through its lower position, of 

 leverage, or, more strictly speaking, of obliquely upward thrust, 

 against the borders of the continents. 



(2) That among mountain elevations there are those which, 

 like the Alleghanies, are the result of one process of making, or 

 monogenetic, and those that are a final result of two or more 

 processes at different epochs, or are po ly genetic. 



(3) That there are two kinds of monogenetic ranges : — those 

 that are geanticlinals, or anticlinoria, like the region of the Cin- 

 cinnati uplift ; and those that were the result of a slowly pro- 

 gressing geosynclinal, with consequently a very thick accumu- 

 lation in the trough of sedimentary beds, ending in an epoch of 

 displacements and solidification, and often of metamorphism of 

 the sedimentary beds, as in the case of the Alleghanies and other 

 synclinoria. 



(4) That great mountain-chains are combinations of syncli- 

 noria and of anticlinorian elevations. 



(5) The principle advocated by LeConte (restricted as indi- 

 cated), that plication, shoving along fractures, and crushing are 

 the true sources of the elevation that takes place during the 

 making of the second of the two kinds just mentioned of mono- 

 genetic mountain-ranges or synclinoria. 



(6) That on the oceanic side of the progressing geosynclinal 

 referred to there has been generally, as the first effect of the 

 thrust against the continental border, a progressing geanticlinal 

 which usually disappeared in the later history of the region — 

 gravity, and the yielding and plication in the region of the 

 geosynclinal, favouring this disappearance. 



