THE ORIGIN OF MOUNTAINS. 
57 
fore the Jurassic period, for rolled pebbles of it 
occur in that rock. On the other hand, the fold on 
the summit of the Windgiille contains Eocene strata. 
The origin of the Porphyry then is earlier than the 
Jurassic; the elevation of the mountain is later than 
the Eocene. It is clear, therefore, that the Porphyry 
had nothing whatever to do with the origin of the 
Windgiille mountain. 
The igneous rocks have moreover produced no 
effect on the strata which now rest on them. If, 
however, they had been intruded in a molten con- 
dition, they must have modified the rocks for some 
distance around. It is evident therefore that the 
igneous rocks had cooled down before the overlying 
strata were deposited. The elevation of the Alps 
only commenced in the Tertiary period, but we know 
that the Granite of the southern Alps is, for the most 
part, pre- Carboniferous, that the Porphyry of Botzen 
belongs to the Permian period, the younger Porphyry 
to the Trias, and that the Gneiss of the central range 
of the eastern Alps is still older; it is evident then, 
that these plutonic rocks can have taken no active 
part in the upheaval of the Alps, which occurred so 
much later. 
We may, indeed, lay it down as a general pro- 
position that folded mountains are not due to volcanic 
