504 J. A. DRESSER IGNEOUS ROCKS OF EASTERN QUEBEC 



specimen of the essentially similar rock from the quarry at Sherbrooke, 

 which furnishes road metal for the streets of that city : 



SiO, 70.37 



TiO, 17 



Al a 8 11.27 



F a O, 80 



FeO 2.58 



MgO 2.03 



CaO 2.31 



Na a O 2.63 



K a O 1.86 



CO, 3.60 



H a O 1.96 



99.58 



The large amount of CO 2 shows the rock to be too far altered to be 

 satisfactorily classified according to the quantitative classification. 

 Neglecting C0 2 , however, the following is the norm: 



Q 38.34 



or 11.12 



ab 22.01 



an 11.40 



C 82 



hyp 8.00 



mt 1.16 



il 30 



Class I, Persalaue. 

 Order 3, Columbare. 

 Rang 3, Riesenase. 

 Subrang 4, dosodic. 



In the thin-section it is found to be a porphyritic rock with a finely 

 crystalline base, which contains phenocrysts of quartz and feldspar. The 

 latter are both orthoclase and plagioclase, the former being the more 

 abundant. 



Small rod-like bodies of colorless mica are present in the rock, as well 

 as irregular areas of a rhombohedral carbonate which is apparently dolo- 

 mite. 



Near Lennoxville, on the line of the Canadian Pacific railway, the rock 

 becomes a granite porph}oy, differing from the rock just described chiefly 

 in the more advanced character of its crystallization. Farther eastward, 

 where this belt is somewhat wider, the central portion becomes still more 

 coarsely crystalline and passes from quartz porphyry at the margin to 



