On the Transition Kocks of the Cataraqui. 235 



the St. Lawrence, and is split into the Thousand Islands, before it 

 sweeps onward towards the Rocky Mountains, the true Andes of 

 North America. 



The want of altitude in the Lacustrian chain, is very remarkable, 

 until it reaches Lake Superior, where the transition limestones are 

 not so observable, and where igneous agency is more apparent. 



It is well known, that the greater portion of the United States 

 and of Canada, is decidedly, either of the transition or secondary 

 class, and that the beds of these rocks are there of enormous thick- 

 ness, and are either very little elevated above the ocean, or in many 

 places below its level, whilst the primary rocks are comparatively of 

 little extent in those regions, and never lofty. 



If it be true therefore, as Bakewell has ingeniously advanced, 

 that volcanic action does not always (and perhaps it never does,) 

 take place, in what we have hitherto considered the lowest rock 

 formation or granite ; from what an inconceivable depth must that 

 action have originated in this vast tract of country, and how likely 

 that it formed the low ridges of the Lacustrian range, by a partial 

 upheaving of the older transition rocks which it occasionally pierced 

 through, and what extraordinary power must have been exerted 

 where it has fractured the granite and its superincumbent beds, to 

 eject and form recognized trap. 



Bakewell observes, that in Auvergne and a large part of Cen- 

 tral France, granite is the foundation rock, and that it has been pier- 

 ced through by numerous ancient volcanoes, which have poured 

 currents of lava over its surface, and covered other parts with loose 

 scoria and black volcanic sand, some of the currents of lava appear- 

 ing as fresh as the recent ones from Etna or Vesuvius. In other 

 parts of Auvergne, he thinks, only, that the granite has been acted 

 upon by subterraneous fire in situ, and in some mountains, as in the 

 Pay de Chopine near Rione, granite and volcanic rocks are inter- 

 mixed, one part being true granite, and the other volcanic porphy- 

 ry, or trachyte, and this is also the case on Lake Superior. 



Where the seat of the igneous agency is very deep, as it no 

 doubt is, in the enormous basin of North America, and covered by 

 the primary rocks and their superincumbent masses, it would be not 

 at all unlikely, that in travelling to find a vent for the pent up gases, 

 it would upheave and finally crack long tortuous lines, spending the 

 utmost of its force wherever it formed spiracles by which to eject its 

 confined vapors. 



