RCCKS. 



251 



the same elements, but grouped d.rFerently, are still formed 

 by volcanic processes, as in the earliei periods of the world. 

 The character of rocks, as we have already remarked, is so 

 independent of geographical relations of space.* that the 

 geologist recognises with surprise, alike to the north or the 

 south of the equator, in the remotest and most dissimilar 

 zones, the familiar aspect, and the repetition of even the 

 most minute characteristics in the periodic stratification of 

 the silurian strata, and in the effects of contact with augitic 

 masses of eruption. 



We will now enter more fully into the consideration of the 

 four modes in which rocks are formed the four phases of 

 their formative processes manifested in the stratified and 

 unstratified portions of the earth's surface ; thus in the en* 

 dogenous or erupted rocks, designated by modern geognosists as 

 compact and abnormal rocks, we may enumerate the following 

 principal groups as immediate products of terrestrial activity. 



1. Granite and syenite of very different respective ages; the 

 granite is frequently the more recent, f traversing the syenite 

 in veins, and being in that case the active upheaving agent. 

 " Where the granite occurs in large insulated masses of a faintly 

 arched ellipsoidal form, it is covered by a crust or shell cleft 

 into blocks, instances of Avhich are met with alike in the Hartz 

 district, in Mysore, and in Lower Peru. This sea of rocks 

 probably owes its origin to a contraction of the surface of the 

 granite, owing to the great expansion that accompanied its 

 first upheaval."^; 



Both in Northern Asia. on the charming and romantic 

 shores of the Lake of Kolivan, on the north-west declivity of 

 the Altai mountains, and at las Trincheras, on the slope of 

 the littoral chain of Caracas, || I have seen granite divided into 

 ledges, owing probably to a similar contraction, although the 



* Loop, von Buch, op. cit. p. 9. 



t Berahard Cotta, Geognosie, 1839, s. 273. 



t Leop. von Buch, Ueber Granit und Gneiss, in the AWiandl. der 

 Berl. Akad., for the year 1842, s. 60. 



In the projecting mural masses of granite of Lake Kolivan, divided 

 into narrow parallel beds, there are numerous crystals of feldspar and 

 albite, and a few of titanium, (Humboldt, Asie centrale, t. i. p. 295; 

 Ouslav Eose, Reise nach dem Ural, bd. i. s. 520 



K Humbotdt, Relation historiqui, t. ii. p. 99. 



