THE OTTAWA NATURALIST. 



Vol. X. OTTAWA, OCTOBER, 1896. No. 7. 



PETROGRAPHICAL NOTES ON SOME ARCHAEAN 

 ROCKS FROM CHELSEA, QUE. 



By John A. Dresser, M.A. 

 Principal of St. Francis College, Richmond, Que. 



No. I. SERPENTINE LIMESTONE.* 



By the aid of the microscope this rock is seen to consist 

 essentially of the minerals calcite and serpentine, and to have 

 muscovite and a few grains of iron ore as accessory constituents. 



The calcite is wholly cr^'stalline and shows rhombohedral 

 cleavage throughout. It is more or less turbid in some parts, 

 evidently from the presence of small inclusions of graphite-like 

 matter, which are elsewhere absent. Such inclusions, when they 

 occur in well-defined areas, are indicative of fossil origin, and 

 even their presence in irregular aggregations may be so inter- 

 preted. 



In this specimen, however, the inclusions appear in gradually 

 varying quantities in a part of the section, but nowhere in areas 

 having any definite boundaries. They are in fact, only more or 

 less freely disseminated through parts of the rock, but not in 

 such a way as to give any satisfactory evidence of an organic 

 origin of the calcite, which may therefore be considered a 

 secondary constituent. 



The serpentine is colorless, except in polarized light, when 

 it shows dull colors and aggregate polarization. It occupies 

 somewhat rounded areas, which have rather uniform boundary 

 lines. 



*Nos. I and 3 are from " the Ravine," Old Chelsea, Que. No. 3 rock is from 

 a 4 to 7-inch dyke cutting No. i. No. 2 is from the first railway cutting north of 

 Chelsea Station, Gatineau Valley Railway. These specimens were all collected by 

 Dr. Ami. The microsections'were prepared by Mr. McNamee, of Buffalo, N.Y. 



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