Section III, 1887. [ 45 ] Trans. Roy. Soc. Canada. 



VII. — Microscopic Petrography of the Drift of Central Ontario. 



By k.V. Coleman. 



(Communicated by Dr. T. S. Hunt, May 25, 18S7.) 



Microscopic petrography is being so eagerly studied, and affords such iuterestiug 

 results in all lauds at the present day, that no apology is necessary for the present contri- 

 bution toward a subject hitherto but little cultivated in Canada. Where so much of the 

 region is petrographically terra incognita, perhaps no better beginning could be made than 

 with the materials so profusely supplied by the drift of Ontario, which offers specimens 

 of an immense variety of rocks derived from various distances to the north and east, and 

 especially representing the Laurentian region. By way of foundation, and for the sake of 

 comparison with the results brought out by the masterly works of Rosenbusch, Zirkel, 

 von Lasaulx, and a host of other enthusiastic students of this most recent of the sciences, 

 a somewhat comprehensive discussion of the microscopic characters of our rocks may be 

 permitted ; so that much that is well known will be briefly sketched, while special atten- 

 tion will be paid to features that appear to be new or unusual. It should be stated that 

 the specimens examined have been collected at various points in Central Ontario, but 

 chiefly in the vicinity of Cobourg ; and it may be added that the merely mechanical work 

 of preparing the 150 rock sections required has been by no means inconsiderable. 



I. — General Description of the Drift. 



As exposed along water-courses and lake shores, the drift is seen to consist of clay, 

 sand, gravel and boulders, the finer materials often laminated, sometimes oblic|uely, 

 with a false bedding resulting from the action of shifting currents. In other cases 

 there is no stratification, and clay, sand and gravel, with intermixed boulders, lie 

 pell-mell where dropped by the melting of ice. The underlying Silurian limestone is 

 polished and striated, the striations near Cobourg running nearly east and west (S. 80° 

 or 85° E., magnetic), with the thrust from the east. " Soled " boulders with one or 

 more flat striated surfaces shew the tools with which the work was done. 



Sands. — Examined with the microscope, the sands prove to contain, in addition 

 to sharp-edged particles of quartz, a large amount of calcareous matter and small 

 fragments of plagioclase, perhaps, also, orthoclase and green or brown hornblende — 

 shewing their origin in the massive and schistose rocks. 



Gravel. — Imbedded in the sand and clay, or forming independent strata, are 

 subaugular or rounded pebbles, more than half of them limestone, the rest of various 

 Laurentian rocks. The shape of the pebbles is determined by the cleavage of the parent 



