Some Dykes cutting Laurentian Series. 483 



the district adjacent to the locality in which the mineral 

 perthite was first discovered. 1 



Thin sections of the scapolite-pyroxene and micro- 

 perthite-pyroxene rocks referred to have a general resem- 

 blance to each other when examined under the microscope 

 in ordinary transmitted light. The pyroxene has about 

 the same form and green colour, occurs in about the same 

 proportion, and is set in a colourless matrix in each. In 

 polarized light, however, the resemblance ends, the scapo- 

 lite possessing very much brighter colours than the 

 feldspar. 



Masses of gabbro and norite are found at a number 

 of localities throughout the district traversed. These 

 coarse-grained rocks possess the same general characters 

 as those of their class which have been described from 

 other parts of Canada. In most of the masses a con- 

 siderable differentiation is shown ; in one part they may 

 show the characters of a normal gabbro while in others 

 they are true norites ; and again, in certain portions of 

 the mass free silica may be present. The gabbro-norite 

 mass which crosses the railroad a short distance north of 

 the village of Parham is interesting on account of the 

 comparatively large size of the inclusions which occur in 

 both the diallage and hypersthene. This rock appears to 

 offer a good opportunity for the determination of the 

 characters of these materials which, except in size, are 

 similar in appearance to those commonly found in these 

 minerals. Prof. Judd, the late Prof. G. H. "Williams, 

 and others, have examined such inclusions in rocks from 

 different parts of the world. In some rocks they have 

 been held to be of secondary origin, while in others it is 

 claimed they are original constituents. Their chemical 

 composition is said to be different in different cases. 



Dykes of the basic rocks occur in great numbers 



1 This rock seems to resemble one referred to by Prof. K. de Kroustchoff, of St 

 Petersburg, Bulletin Soe. Franc, de Min., IX., 1886. Tschermak's Min., u Pet. Mitth. 



