180 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



Three quarters of a mile from the exposure where the specimens 

 whose characters have just been given were collected, there occurs, 

 on the opposite side of the bay in the line of the sti-ike of the dyke, 

 another exposure of the same dyke. On the islands of the bay 

 which lie intermediate between these two localities the outcrop of 

 the dyke is observable, so that there is no doubt of their both 

 being exposures of the same dyke. The rock here was not studied 

 in so great detail as at the last exposure. The specimens taken 

 were of the same grade of coarseness as those taken at 20 feet from 

 the contact on the north side of the bay. The feldspars are more 

 decomposed and the twinning lamellae often obscure, and the small 

 quantity of quartz which is associated with them appears to be of 

 secondary origin ; whereas the origin of the quartz noted in the same 

 dyke on the north side of the bay seemed much more problematic. 

 In the latter case the common micropegmatitic character of the 

 quartz and the occurrence in it of needles of apatite, which in no 

 way differ from those in the feldspar, together with the not 

 infrequent occurrence of one individual of apatite partially included 

 in quartz and partially in an adjacent I'eldspar, would argue for 

 the j)rimary character of the quartz. The augite in the dyke on 

 the south side of the bay resembles that already described occur- 

 ring both in simple individuals and in polysomatic masses. It is 

 largely altered to uralite. Titanic iron with its alteration product 

 leucoxene shows characteristic barred structure of the cleavage traces 

 parallel to the planes of the rhombohedron. The leucoxene 

 is frequently accompanied by a mai-gin more or less extensive, of 

 secondary brown mica. Apatite is present in comparative abundance. 

 Chlorite occurs in vaguely defined masses and the garnets which, as 

 before, are present, are associated with it. 



On the south-east shore of Pipestone Lake about a mile west of 

 Stone-dam Portage occurs another of these dykes cutting transversely 

 schists which have a strike of N.E. to E.N.E. The specimen taken 

 fi'om the middle of the dyke has the characters of an uralitic quartz 

 diabase. The feldspar as a rule is i-emarkably fresh and occurs in 

 the usual lath-shaped twinned crystals of plagioclase. The crystals 

 are commonly observed to be cracked transversely and the cracks 

 filled with a brownish yellow mateidal which shows aggregate 



