19S Common RocJcs of the British Provraces. 



between Brockville and King-ston, and penetrates the State of New York to 

 the neighbourhood of Lake Champlain. The whole of this vast tract of 

 country consists ahnost altogether of stratified rocks composed of these four 

 minerals, quartz, felspar, mica, and hornblende, with here and there a band 

 of white crystelline limestone. Were all the forests and all the loose soil to 

 be swept away from the formation, so that the actual solid crust of the globe 

 could be seen, and were a spectator to be so placed above the earth that he 

 could take a bird's-eye view of the whole region at one glance, the surface 

 would appear to him to be constituted of multitudinous thin leaves of rock 

 twisted and folded in every direction. These leaves would be the strata of 

 gneiss, schist, or limestone, which form the great mass of the Laurentian 

 system, and their twistiugs and foldings the effects of the ancient convulsions 

 of nature by which they, although of the strongest rock, have been shrivelled 

 up as a scroll. 



The most abundant rock of the Laurentian STstem is what is called 

 Syenitic gneiss, and in order to shew wherein this differs from granite, we 

 shall give the following description of the origin and composition of these 

 and a few others that will frequently be met with in Canada. 



Granite. — This rock is composed of quartz, felspar, mica, and sometimes 

 hornblende, and is of several varieties, such as — 1st. Granite, properly so 

 called, consisting of quartz, felspar, and mica. 2ud. Graphic granite, com- 

 posed of quartz and felspar only, but so arranged as to produce an irregular 

 laminar structure. When cut and polished in a direction across the plates 

 of quartz and felspar, of which it consists, the surface of graphic granite 

 appears to be covered with Hebrew letters inlaid and blended into the 

 substance of the rock. Hence its name : 



3rd. Porphyritic granite, which, in addition to the usual ingredients, 

 contains distinct large crystals of felspar. 



4th. Syenitic granite, composed of all four of the minerals, quartz, 

 mica, and hornblende. 



There are numerous other varieties, but the above are all we need notice 

 for our present purpose, and they are all supposed to have been once in a 

 fluid state and to have become consolidated by cooling. The true geological 

 position of granite appears to be beneath every other species of rock, although 

 it is often seen upon the siu-face, having been ejected, while fluid, thrust up 

 through the others in solid masses, or uncovered by the removal of the once 

 overlying formations. Sir Charles Lyell says, " all the various kinds of 

 granite which constitute the plutonic family, are suj^posed to be of igneuos 

 origin, but to have been formed under great pressures at a considerable depth 

 in the earth, or sometimes, perhaps under a certain weight of incumbent 

 water. Like the lava of volcanoes, they have been melted, and afterwards 

 cooled and crystalised, but with extreme slowness, and under conditions very 

 difterent from those of bodies cooling in open air." A large proportion of 

 the interior of the earth may therefore be granite; probably solid tovrards 

 the surface where it supports the stratified rocks and fluid below. Pluto, a 

 god of the ancients, was said to be the king of the lower regions, and hence 



