46 Shrinkage and 



(figs. 3, 12, and 57). This, according to the theory long 

 ago proposed by Elie de Beaumont, and adopted by 

 De la Beche in his ' Eesearches in Theoretical Geology,' 

 is the origin of mountain chains. After water took its 

 place on the earth, by such processes land was again and 

 again raised within the influence of atmospheric disin- 

 tegration, and rain, rivers, and the sea, acting on it, 

 were enabled to distribute the materials of sedimentary 

 strata. Such disturbances of strata have been going 

 on through all known geological time, and I firmly 

 believe are still in progress. 



Such shrinkage and crumpling, where it has been 

 most intense and on the greatest scale, is often (where 

 I know it) accompanied by the appearance of gneissic 

 or other metamorphic rocks, and often of granite or its 

 allies. 



The oldest rock in the British Islands is gneiss, 

 but that originally was doubtless a common stratified 

 formation of some kind or other. In fact, as far as the 

 history told by the rocks themselves informs us, we 

 cannot get at their beginning, for all strata have been 

 made from the waste of rocks that existed before ; and 

 therefore the oldest stratified rocks, whether metamor- 

 phosed or not, have a derivative origin. 



I must now briefly endeavour to give an idea of the 

 theory of metamorphism. The simplest kind is of that 

 nature mentioned in Chapter I. namely, when melted 

 matter has been forced through or overflows a stratified 

 rock, and remaining for a time in a melted state, an 

 alteration of the stratified rock in immediate contact 

 with it takes place. Thus sandstone may, by that 

 process, become converted into quartz-rock, which is 

 no longer hewable, like ordinary sandstone, but breaks 

 with a hard and splintery fracture. Here then rocks 



