
~ Parr VIL Sucr.i.§ 1.] ERUPTIVE GRANITE. B41 
_ other rocks, as in the Piz de Graves in the upper Engadine, where 
a wall-like mass of granite, with syenite, diorite, and altered rocks, 
may be seen resting upon schists." In the Alps and other moun- 
tain ranges it is found hkewise in large bed-like masses which run 
in the same general direction as the rocks with which they are 
associated. 
Relation of Granite to contiguous Rocks.—From an 
early period the attention of geologists has been given to the evident 
mineralogical change which has taken place among stratified rocks 
as they approach a mass of granite. This change has been specially 
studied in some Huropean areas, of which those of the Vosges, the 
Hartz, Devon and Cornwall, Treland, Scotland and Norway, are well 
known. ‘The nature of the metamorphism thus superinduced upon 
rocks is more particularly discussed at p. 578. : 
The south-east of Ireland supplies an admirable illustration of the - 
relation between granite and its surrounding rocks (Fig. 269). A mass 
of granite 70 miles in length and from 7 to 17 in width there stretches 
from north-east to south-west, nearly along the strike of the Lower 
Silurian rocks. These strata, however, have not been upraised by it in 
such a way as to expose their lowest beds dipping away from the granite. 
On the contrary, they seem to have been contorted prior to the appearance 
of that rock; at least they often dip towards it, or lie horizontally or 
undulate upon it, apparently without any reference to movements which 


Fic. 269.—Secrion ACROSS PART OF THE GRANITE BELT oF THE SouTH-E\AsT oF IRELAND. 
a, Granite; 6 b, patches of Lower Silurian rocks lying on the granite at various 
distances from the main Lower Silurian area, ¢ ¢. 
it could have produced. As Mr Jukes has shown, the Silurian strata are 
underlaid by a vast mass of Cambrian rocks, all of which must have been 
invaded by the granite before it could have reached its present 
horizon.. He infers that the granite must have slowly and irregularly 
eaten its way upward through the Silurian rocks, absorbing much of 
them into its own mass as it rose. For amile or more the stratified beds 
next the granite have been altered into mica-schist, and are pierced by 
numerous veins from the invading rock. Within the margin of the granitic 
mass belts or rounded irregular patches of schist (b 6) are enclosed ; 
but in the central tracts where the granite is widest, and where there. 
fore we may suppose the deepest parts of the mass have been laid bare, no 
such included patches of altered rock occur. From the manner in which 
the schistose belt is disposed round the granite, it is evident that the 
upper surface of the latter rock where it extends beneath the schists 
must be very uneven. Doubtless the granite rises in some places much 
nearer to the present surface of the ground than at others, and sends out 
veins and strings which do not appear above ground. If, as Mr Jukes 
supposes, a thousand feet of the schists could be restored at some parts 
* Studer, “ Geologie der Schweitz,” i. p. 290. 
