578 VOLUME OF HIDDEN PLUTONIC ROCKS. [Ch. XXXIV. 



But the theory adopted in this work of the subterranean origin of the 

 hypogene formations would be untenable, if the supposed fact here 

 alluded to, of the appearance of tertiary granite at the surface was not 

 a rare exception to the general rule. A considerable lapse of time must 

 intervene between the formation, in the nether regions, of plutonic and 

 metamorphic rocks, and their emergence at the surface. For a long 

 series of subterranean movements must occur before such rocks can be 

 uplifted into the atmosphere or the ocean ; and, before they can be ren- 

 dered visible to man, some strata which previously covered them must 

 usually have been stripped off by denudation. 



We know that in the Bay of Baiae, in 1588, in Cutch in 1819, and 

 on several occasions in Peru and Chili, since the commencement of the 

 present century, the permanent upheaval or subsidence of land has been 

 accompanied by the simultaneous emission of lava at one or more points 

 in the same volcanic region. From these and other examples it may be 

 inferred that the rising or sinking of the earth's crust, operations by 

 which sea is converted into land, and land into sea, are a part only of 

 the consequences of subterranean igneous action. It can scarcely be 

 doubted that this action consists, in a great degree, of the baking, and 

 occasionally the liquefaction, of rocks, causing them to assume, in some 

 cases a larger, in other a smaller volume than before the application of 

 heat. It consists also in the generation of gases, and their expansion 

 by heat, and the injection of liquid matter into rents formed in 

 superincumbent rocks. The prodigious scale on which these subterranean 

 causes have operated in Sicily since the deposition of the Newer 

 Pliocene strata will be appreciated, when we remember that throughout 

 half the surface of that island such strata are met with, raised to the 

 height of from 50 to that of 2000 and even 3000 feet above the level 

 of the sea. In the same island also the older rocks which are contiguous 

 to these marine tertiary strata must have undergone, within the same 

 period, a similar amount of upheaval. 



The like observations may be extended to nearly the whole of Europe, 

 for, since the commencement of the Eocene period, the entire European 

 area, including some of the central and very lofty portions of the Alps 

 themselves, as I have elsewhere shown*, has, with the exception of a 

 few districts, emerged from the deep to its present altitude ; and even 

 those tracts, which were already dry land before the Eocene era, have 

 almost everywhere acquired additional height. A large amount of 

 subsidence has also occurred during the same period, so that the 

 extent of the subterranean spaces which have either become the 

 receptacles of sunken fragments of the earth's crust, or have been ren- 

 dered capable of supporting other fragments at a much greater height 

 than before, must be so great that they probably equal, if not exceed in 

 volume, the entire continent of Europe. We are entitled, therefore, to 

 ask what amount of change of equivalent importance can be proved to 



* See map of Europe and explanation, in Principles, book L 



