PART II. CHAPTER XXIV. 



291 



Protrusion of Solid Granite. 



suppose that when a small part only of the globe has been inves- 

 tigated, 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 antecedent strata containing 

 organic remains, which may have become metamorphic. If we 

 find pebbles of granite in a conglomerate of the Lower Cam- 

 brian system, we may then feel assured that the parent granite 

 was formed before the Lower Cambrian formation. But if the 

 incumbent strata be merely Silurian or Upper Cambrian, the 

 fundamental granite, although of high antiquity, may be poste- 

 rior 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 deposi- 

 tion of those strata.* Professor Sedgwick and Mr. 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 contact, 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 

 unstratified, 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 inexplica- 

 ble. Thus, for example, at Weinbohla and Hohnstein, near 

 Meissen, in Saxony, a mass of granite has been observed cover- 

 ing strata of the cretaceous and oolitic periods for the space of 

 between 300 and 400 yards square. It appears clearly from a 

 recent memoir of Dr. B. Cotta on this subject,*!" that the 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 secondary rocks. As the granite overhangs both the lias 

 and chalk, so the lias is in some places bent over strata of the 

 cretaceous era. 



Age of the granite of Arran — In this island, the largest in 



* Murchison, Geol. Trans. 2d series, vol. ii. p. 307. 

 t Geognostische Wanderungen, Leipzic, 1838, 



