430 



DESCRIPTION OF THE COUNTRY BORDERING 



chemical constitution, and bedding or stratification, from either the greenstone or 

 black trap. 



Proceeding along the mountain ridges of the northern part of the range, between 

 the main stream and the outlet of Lac des Anglais, we encounter other varieties of 

 rocks, felspathic, granitic, and hornblendic, in their composition, apparently an 

 independent uplift or outburst. Along this whole line, however, the metamorphic 

 rocks of the southern ridges of the range are continuous from near the Montreal to 

 Lac des Anglais. They have, at different times, been pushed over the granites at 

 the south ; distorted, broken, and tilted up in different degrees, but always in the 

 same direction. The northern portion of the range exhibits to my mind evidence 

 of four periods of igneous action ; producing four formations of rocks of a trapjaose 

 cast, which I have represented separately on the map. 



They are : — 1st. Black and red trap ; 2d. Greenstone trap, embracing or gradu- 

 ating into massive hornblende and syenite, at the west ; 3d. Augite and hornblende 

 rocks in mass, also embracing granite and syenite ; 4th. Granite, syenite, and coarse 

 hornblende rocks, north of Lac des Anglais. 



But how to decide the order, or relative age of these protrusions ? It appears 

 that the same materials, under different circumstances of fluidit}', pressure, and 

 rapidity of cooling, may take all these forms. 



At present I can only place these four varieties in one group, filling a geological 

 epoch of no great duration, and place it between the era of the red sandstone 

 deposits and the metamorphic uplifts ; for it is by the appearance of this group that 

 both those systems have been pushed aside, one to the north, the other to the 

 south. Whether the schistose rocks, before their upheaval and metamorphosis, 

 were older or newer than the sandstone, I do not decide ; but both the schists and 

 the unaltered sedimentary rocks are more ancient than the above group numbered 

 from one to four. 



The subdivision which Dr. Houghton and all subsequent geologists call the con- 

 glomerate, is apparently a breccia, resulting from mechanical disturbance of the 

 sandstone by the intruding masses of trap. It probably took place before the 

 overlying sandstone had become indurated, and the reason why the pebbles of trap 

 that compose a large portion of the conglomerate rock are more rounded than is 

 usual in breccias — having even a water-worn aspect — is the extreme agitation that 

 took place. The thickness of the sand-rock is immense, and the passage of other 

 rocks through this distance, always in contact with each other, would give the 

 fragments a rounded form. The protruding granites of the great core of Plutonic 

 rocks in the northern part of the State of New York, has left the Potsdam sandstone 

 in many places in the form of a conglomerate, where the pebbles are granitic. 



On the north shore, in the vicinity of quartz outbursts, through the altered sand- 

 rocks, the crushed masses, next the quartz, have all degrees of roundness, from 

 angular fragments to oblong spheres, according as the motion has been great or 

 small. 



At the Aminekan River the conglomerate extends but a short distance from the 

 trap, wedging out in the course of a few rods, and replaced by the stratified sand- 

 rock. It is never seen far away from the trap, and wherever the junction of the 



