o'20 A. K. BARLOW — LAURENTIAN AND HURONIAN ROCKS. 



slide are numerous scales of brown biotite and a Less proportion of Muscovite. 

 Most of these mica scales have a parallel arrangement, but some are seen to have 

 been developed in the curved lines or areas between the original clastic grains- 

 Some of the quartz grains show evidence of pressure in the optical tension which 

 they manifest under crossed nicols. Inclusions are not abundant iu the quartz." 



Of the second slide he says : 



"A silvery micaceous, very quartzose schist, somewhat rusted, and with strongly 

 micaceous sheen surfaces. Under the microscope the rock is seen to be composed 

 essentially of quartz and muscovite. There is a well-marked parallelism in the 

 arrangement of the muscovite, and the quartz shows distinct cataclastic structure, 

 wavy extinction arrangement in parallel areas and other crush phenomena' 

 e\ idently an altered sandstone." 



Bedding Planes of and intrusive Masses in tin Huronian mica Schists. — The 

 planes of bedding of the Huronian mica schists are parallel to the lam- 

 ination of the gneiss. Both rocks have a strike N. 25° E. and a dip 

 S. -V>° 10. of 75°, the mien schists dipping into or under the gneiss. Pene- 

 trating the schists are lenticular sheets and patches of gneissic material 

 similar in character and composition to the great mass of the gneiss in 

 the immediate vicinity, to which they may often be continuously and 

 directly traced. These intrusions of gneiss have disposed themselves 

 usually in a direction parallel to the bedding of the schists, thus show- 

 ing the coincidence of the lines of least resistance with the lamination of 

 the schists. The intrusive nature of these gneissic patches and sheets is 

 quite evident from even a cursory examination of the relations of the 

 two rocks in situ, for the foliation of the gneiss composing these intrusions 

 is parallel to the walls of the fissures even when these fissures cross the 

 strike of the schists. This also seems to demonstrate that gneissic lam- 

 ination is caused by the flow of the rock under differential pressures. 

 Angular fragments of the Huronian mica schists are included in the 

 gneiss, the foliation of the latter conforming roughly with the irregular 

 outlines of the fragments, the flow structure thus produced being always 

 very marked. 



Microscopic Examination of Quartzite and granitoid Gneiss. — There was 

 obtained from this locality a hand specimen, which, before being sliced, 

 showed a dark greenish-gray fine-grained quartzite, with two small hands 

 of.granitoid gneiss irruptive through it. Dr Lawson thus describes it : 



"Under the microscope the quartzite is a typical epiclastic rock, presenting no 

 strong evidence of deformation by pressure. It consists of a heterogeneous aggre- 

 gate of clastic grains of quartz and feldspar, much of the latter being plagioclase. 

 I n sections the shape of these grains is rounded, subangular, or sometimes angular. 

 The larger grains are embedded in a base composed of much smaller mains of the 

 same materials, but intimately mixed with a green chloritic substance, which gives 

 its color to the rock. The section crosses the contact of the granite stringer and 



