On the Norian or "Upper Laurentian " Formation. 295 



the southern part of the area. The results were published 

 in the Report of the Geological Survey of Canada for the 

 year 1857. Abbe Lanamme likewise gives a brief descrip- 

 tion of a few exposures in the Geological Survey Report 

 for 1884. Richardson gives a general description of the 

 anorthosite of the southern part of the area, but his 

 statements concerning the western limit as well as his 

 estimate concerning its extension towards the north are 

 erroneous. He, however, pointed out in his work the 

 resemblance of the character of these rocks to those of 

 other parts of Canada, and thus increased by one the 

 number of such areas already known in other parts of the 

 Laurentian. 



The anorthorsite of this "Saguenay area," as we shall 

 call it, consists, like that of the Morin area, of a basic 

 plagioclase. The latter is sometimes labradorite, some- 

 times bytonite. Augite, hypersthene, and at times also 

 hornblende and biotite are other constituents ; they are 

 in every respect identical with the corresponding minerals 

 of the Morin area, and therefore require no special descrip- 

 tion. The rock is of medium grain, but the coarseness of 

 grain varies considerably and often quite abruptly from 

 place to place. The crystals of the coarse granular 

 varieties frequently increase in size till the plagioclase 

 individuals reach a foot or more in diameter. 



A difference between this anorthosite and that from 

 the Morin area consists in the fact that the former often 

 contains olivine. This mineral occurs often in considerable 

 quantity, so that there results a plagioclase-olivine rock 

 or Troctolite, in which all other iron-magnesia compounds 

 are wanting, with the exception of those forming the 

 zones of corrosion at the contact of the olivine with the 

 plagioclase. These zones, which occur so frequently in 

 the gabbro, have nowhere else been observed in a more 

 perfect development. Even in the field, an orange 

 weathering constituent invariably surrounded by a narrow 



