280 Canadian Record of Science. 



one showing those irregular coarse-grained patches to one 

 with an imperfect banding like that observed in the 

 Morin area, is found in the Saguenay anorthosite area 

 along River Shipshaw, which, coming from the north, 

 empties into the Saguenay about seven miles above 

 Chicoutimi. 



Along this stream many large smooth surfaces or 

 " Eoches Montonnees " of anorthosite are exposed which 

 has been superficially etched by the atmospheric agencies 

 and whose vegetable growth has completely been removed 

 by forest fires, so that the structure of the rock is excel- 

 lently displayed. This series of exposures is limited on 

 the north by a colossal dyke of gabbro, nearly half-a-mile 

 wide, and which^cuts the anorthosite, enclosing fragments 

 of it. The exposures can be studied for a distance of eight 

 miles in a straight line down the Shipshaw River to a 

 point which is three miles distant from its mouth in the 

 Saguenay. 



At first the rock is coarsely granular, and over the 

 whole extent of the large exposures is quite massive and 

 of uniform composition. It is exposed thus for about 

 half-a-mile, and then spots or patches, which must be 

 designated as very coarse-grained, commence to appear. 

 In these coarse-grained portions the individual grains are 

 an inch or more in size, while they are much smaller in 

 the rest of the rock. Both show a very distinct ophitic 

 or diabase structure, that is to say, the plagioclase occur 

 in lath-shaped forms whose interstices are filled up with 

 augite. The structure continues for four miles, with, in 

 places, an additional irregularity caused by local variations 

 in the relative proportion of certain of the constituents. 

 There are, for example, considerable exposures where the 

 rock consists entirely of plagioclase, while in other places 

 much diallage is present in masses as much as 1J foot in 

 diameter. Large masses of almost pure plagioclase or 

 diallage also occur in places in the normal rock. 



