Ch. XXXIV.] PROTRUSION OF SOLID GRANITE. 727 



Cambrian strata resting immediately on granite, there being no alter- 

 ations at the point of contact, nor any intersecting granitic veins, we 

 might then affirm the plutonic rock to have originated before the 

 oldest known fossiliferous strata. Still it would be presumptuous, as 

 we have already pointed out (p. 587), to suppose that when a small 

 part only of the globe has been investigated, we are acquainted with 

 the oldest fossiliferous strata in the crust of our planet. Even when 

 these are found, we cannot assume that there never were any ante- 

 cedent strata containing organic remains, which may have become 

 metamorphic. If we find pebbles of granite in a conglomerate of the 

 Lower Cambrian system, we may then feel assured that the parent 

 granite was formed before the Lower Cambrian formation. But if the 

 iucumbent strata be merely Silurian or Upper Cambrian, the funda- 

 mental granite, although of high antiquity, may be posterior in date 

 to known fossiliferous formations. 



Protrusion of Solid Granite. — In part of Sutherlandshire, near 

 Brora, common granite, composed of felspar, quartz, and mica, is in 

 immediate contact with Oolitic strata, and has clearly been elevated 

 to the surface at a period subsequent to the deposition of those strata.* 

 Professor "Sedgwick and Sir R. Murchison conceive that this granite 

 has been upheaved in a solid form ; and that in breaking through the 

 submarine deposits, with which it was not perhaps originally in con- 

 tact, it has fractured them so as to form a breccia along the line of 

 junction. This breccia consists of fragments of shale, sandstone, and 

 limestone, with fossils of the oolite, all united together by a calcareous 

 cement. The secondary strata, at some distance from the granite, are 

 but slightly disturbed, but in proportion to their proximity the amount 

 of dislocation becomes greater. 



If we admit that solid hypogene rocks, whether stratified or un- 

 stratified, have in such cases been driven upwards so as to pierce 

 through yielding sedimentary deposits, we shall be enabled to account 

 for many geological appearances otherwise inexplicable. Thus, for 

 example, at Weinbohla and Hohnstein, near Meissen, in Saxony, a 

 mass of granite has been observed covering strata of the Cretaceous 

 and Oolitic periods for the space of between 300 and 400 yards 

 square. It appears clearly from a memoir of Dr. B. Cotta on this sub- 

 ject,! that ^ ne granite was thrust into its actual position when solid. 

 There are no intersecting veins at the junction — no alteration as if by 

 heat, but evident signs of rubbing, and a breccia in some places, in 

 which pieces of granite are mingled with broken fragments of the sec- 

 ondary rocks. As the granite overhangs both the lias and chalk, so 

 the lias is in some places bent over strata of the cretaceous era. 



Relative Age of the Granites of Arran. — In this island, the largest 

 in the Firth of Clyde, being twenty miles in length from north to 



* Murchison, Geol. Trans., Second Series, vol. ii. p. 307. 

 f Geoguostische Wanderungen, Leipzig, 1838. 



