TYPICAL LAURENTIAN AREA OF CANADA. 327 



rocks was considered, in all cases, to be a more or less obliterated 

 survival of original bedding. The detailed mapping in the field, 

 accompanied by microscopical work ip the laboratory, by which 

 alone conclusive results can be obtained in working out the 

 structure of complicated areas of crystalline schists, was not car- 

 ried out, in fact in many districts the construction of detailed 

 maps was at that time practically impossible. It is not surprising 

 therefore that, although excellent in the main, some of the 

 results arrived at have since proved to be erroneous. 



It is proposed, in the present paper, to place before the read- 

 ers of this Journal in as brief a manner as possible, a general 

 account of the several series of rocks occurring in this area, and 

 to point out what, in the opinion of the present writer, seems to 

 have been satisfactorily established concerning the statigraphical 

 position and mutual relations of these ancient rocks and what 

 still remains to be determined by further study, and in conclu- 

 sion to give a short sketch of the evolution of this portion of the 

 continent. 



Tlie Fundamejital Gjieiss. — Exposed over very wide stretches 

 of country in Canada, and making up in all probability by far the 

 larger part of the Archean Protaxis, is the "Fundamental 

 Gneiss," sometimes called, from its - great development about 

 the upper waters of the Ottawa River, the "Ottawa Gneiss." It 

 is composed essentially of orthoclase gneiss, usually reddish or 

 greyish in color. Of this there are a number of varieties, differ- 

 ing from one another in size of grain, relative proportion of 

 constituent minerals and in the distinctness of the foliation or 

 banding. It is sometimes rich in quartz, while at other times 

 this mineral is present in but very small amount. It is usually 

 poor in mica and bisilicates. Dark bands of amphibolite are not 

 uncommon, while basic hornblende or pyroxene gneisses occur 

 in some places. Other schistose rocks are rarely found. Over 

 great areas it is often nearly uniform in character and possesses 

 a foliation which can only be recognized when exposures of con- 

 siderable size are examined. On this account it is often referred 

 to as a granitoid gneiss, a designation, however, which by no 



