1899] Barlow— A RCH^AN Conglomerates. 215 



bands along the planes of fissility in the schist, is often many- 

 times in excess of the breadth at right angles to the foliation. 

 Indeed many of the outcrops representing the less modified 

 phase of these rocks, very closely resemble exposures of the 

 highly differentiated and parallel alterations of basic and acidic 

 bands so persistently typical of the granite and diorite gneisses 

 usually classed as Laurentian. The wider and more continuous 

 of these more acid portions agree very closely with pegmatite in 

 structure and composition, while the narrow dykes which greatly 

 prevail are micro-granitic in appearance. 



Under the microscope, thin sections show these fine-grained 

 felsitic looking dykes to be composed of a micro-crystalline or 

 granulitic aggregate, made up, it may be presumed of quartz and 

 felspar, resembling very closely the groundmass of certain quartz 

 porphyries. Cataclastic structure is so pronounced that all trace 

 oflargcr individuals, if originally present, has disappeared and a 

 very fine-grained mosaic, of sharply extinguishing felspar and 

 quartz individuals, which are very difficult to distinguish from one 

 another, remains. There is a very much smaller quantity of decom- 

 posed biotite, most of which occurs in dark wavy lines represent- 

 ing mechanically disintegrated portions of this mineral, producing 

 in the rock a very recognizable micro-fluxion structure. The darker 

 coloured portion of the rock is composed mainly of biotite with 

 occasional scales of muscovitc. Narrow alternating bands are 

 composed of water clear felspar and quartz, while calcite, sur- 

 rounded by larger individuals of quartz and felspar, characterizes 

 certain lenticular areas. Besides these, small inclusions often 

 occur representing the lighter coloured rock or micro-granite 

 around whih the individuals of biotite seemed to "flow " in long 

 gentle curves corresponding very closely with their outline. The 

 junction between the two rocks is rather sharp, but where these 

 intrusions are larger and more numerous, there seems rather pro- 

 nounced evidence of the commingling of the material of both 

 rocks as a result of actual fusion. These are usually lenticular 

 in outline narrowing down at either extremity and exhibiting 

 small veinlcts or tails of quartz, thus revealing their intimate 



