Geology of the Long Lake quadrangle 527 



The analysis seems to warrant the conclusion that the rock is an 

 igneous one, and if that be true the obvious differences between it 

 and the eruptives previously described suggest a separation from 

 them and likely an age difference. 



Pyroxenic amphibolites, hornblende-andesin rocks with acces- 

 sory augite, hypersthene and magnetite, occur in abundance asso- 

 ciated with the distinctive Grenville rocks and have been described 

 by all workers in districts where these rocks occur. They 

 have been sometimes rcgirded as sediments, and sometimes as 

 igneous rocks. The appended analysis is therefore of interest. 

 It is the average of the three best analyses turned in by a class in 

 quantitative analysis, and is therefore not of high grade. In con- 

 sideration of the close supervision however, the close agreement 

 between the three, and the general high character of the work done 

 by the three men, it is thought to be worthy of respect, in con- 

 sideration of the lack of better analyses. The rock was a Grenville 

 amphibolite occurring south of Follensby pond and not far north 

 of Moose creek. 



Si0 2 5 C • 7 x 



A1 2 3 -. 18.75 



Fe 2 3 7.85 



MgO 3.78 



CaO 9.78 



Na 2 4.86 



K 2 2.42 



H 2 0+ 1. 13 



H 2 0— o . 06 



MnO 0.25 



Total '. 99.59 



This is the composition of a diorite, or gabbro, and suggests, 

 though it does not demonstrate, the igneous nature of the rock. If 

 it be igneous it likewise is probably a much more ancient rock than 

 the gabbros of the intrusions. 



