Ivi PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



grandeur, for what has been carried away or borrowed from one space 

 must always have been given to another. The gain must always have 

 equalled the loss, and sediment deposited in one area must be the mea- 

 sure of the quantity of pre-existing rock cleared away elsewhere. The 

 announcement of this principle may seem, perhaps, like insisting on a 

 truism, but I find it necessary, because in many geological specula- 

 tions I observe it is taken for granted that the external crust of the 

 earth has been always growing thicker, in consequence of the accumu- 

 lation of stratified rocks, as if they (and possibly the contemporaneous 

 rocks of fusion, in progress far below) were not produced at the 

 expense of pre-existing rocks, stratified and unstratified. Whether 

 indeed the trap and granite of successive ages were formed by the 

 melting of matter previously solidified, will be questioned by those 

 who contend that the globe was originally a fiised mass, and who 

 also assume (still more gratuitously as appears to me) that geological 

 monuments have reference to the period when the melted nucleus 

 was passing to a more and more solid state. But even those geolo- 

 gists must admit that strata of the old red sandstone, or of any other 

 ancient or modern rock of mechanical origin, imply the transporta- 

 tion from some other region, whether contiguous or remote, of an 

 equal amount of solid material, so that the stony exterior of the 

 planet has always grown thinner in one place whenever by acces- 

 sions of new strata it has acquired density in another. The vacant 

 space left by the missuig rocks, after extensive denudation, may be 

 less imposing to the imagination than a vast thickness of conglo- 

 merate or sandstone, or the bodily presence as it were of a mountain- 

 chain, with all its incHned and curved strata; but the denuded tracts 

 speak a clear and emphatic language to our reason, and hke mountain 

 masses of fossil nummulites, or of corals and shells, or seams of coal 

 based on under-clays full of Stigmaria and surmounted by erect fossil 

 trees, demand countless ages for their origin, and these ages supply 

 the time in which continents and mountain-chains may rise and sink, 

 without sudden, instantaneous or paroxysmal action. 



I have already alluded to the slow crystalhzation and consequent 

 contraction of granitic mixtures, and to the expansion of solid rocks 

 by heat, and to the melting of stony masses, together with various 

 metamorphic agencies, as the causes of slow and gradual movement, 

 both vertical and horizontal. Formerly, when the stratified materials 



