RELATIVE AGE OF THE GRANITES. 25 



deposit of this latter rock. Such a negative argument, how- 

 ever, has not much value. 



The elevation of the central granite mountains to their 

 present height may have been a gradual process, during the 

 continuance of which, in waters constantly becoming 

 shallower, the strata of slate may have been exposed to 

 further extensive denudation, which, joined to various at- 

 mospheric influences, afterwards acting, would give their 

 present form and outline to the jagged ridges of the northern 

 mountains. Long before this elevation took place, the 

 granite, under the pressure of the superincumbent slate, and 

 perhaps of the newer formations also, had acquired its 

 crystalline structure by the slow passage of its heat of fusion 

 into the adjoining strata; and most probably it was quite 

 solidified anteriorly to its elevation, so that it was protruded 

 in a solid form. 



14. The agent in this protrusion may have been a newer 

 granite, produced beneath an older. Let fresh accessions of 

 molten matter the matter of granite be slowly and con- 

 stantly transfused from the nether depths, amid the basement 

 portion of the older granite, already cooled and crystalline 

 above, while fused below by contact with the molten mass 

 this latter will expand, and perhaps laterally extend the 

 former, and raise it in a solid form. Thus a great upward 

 movement might be produced, forming the high mountain 

 nucleus of the north, and at the same time elevating and 

 contorting the strata of slate and sandstone resting on the 

 flanks of the older granite, and in some places perhaps even 

 inverting the dip of the slate, as being subject to a greater 

 strain, and more likely to yield en masse, without disruption ; 

 while the sandstones of the southern plateau, remote from 

 the focus of intensity in the upheaving force, would be 

 elevated from below in more horizontal strata. The newer 

 granite from below might likewise impenetrate the older, 

 overflow it in places, and spread out over it; or even break 

 through and impenetrate other strata beyond the limits of 



