516 MR. E. GILPIN ON THE GEOLOGY OE 



between the Lower Silurian or Upper Cambrian of Cape Breton, to 

 be alluded to as probable equivalents of the Lower Potsdam or 

 Lingula Flags, and the series under consideration. 



This formation occupies more than one half of the island. North 

 of the Bras d'Or lake it stretches in a wide belt to Cape St. Law- 

 rence, interrupted only by the Carboniferous of Margaree River and 

 Lake Ainslie, and by narrow fringes of the same strata around the 

 shore and along the valleys of some of the larger streams rising in 

 the centre of the island. Other large areas are occupied by these 

 strata at Cape Mabou, Washabak, Judique, Mira, Boisdale, Cox- 

 heath, and St. Anns, where they rise prominent among the low- 

 lying hills and valleys of the Carboniferous. 



Two divisions have been recognized in these measures. The 

 lower consists of laminated felsites and of interstratified porphyry 

 and syenitic* and gneissoid rocks ; the upper is characterized by the 

 addition of great beds of limestone. Mr. Fletcher, speaking of the 

 lower division, gives it as the result of his experience that both the 

 felsitic and syenitic strata are intimately associated as part of the 

 same group of crystalline rocks, differing not so much in compo- 

 sition as in the degree of crystallization they have been subjected 

 to, and that as no evidence has been found proving the higher posi- 

 tion of the felsites, they may at present be considered together. 



The Washabak hills consist of gneiss, mica-schist, syenite, diorite, 

 hornblende rock, quartzite, and felsite ; all are more or less foliated, 

 and sometimes in exceedingly thin laminae. The Boisdale and Mira 

 hills are made up chiefly of obscurely bedded syenite, with limited 

 areas of other rocks ; the Coxheath hills of alternations of syenite, 

 quartzite, and compact felsite ; and the East Bay hills of felsite, 

 syenite, and granite, in every gradation of colour and texture. In 

 the Boisdale hills this series is represented principally by bluish and 

 grey syenite. The syenite contains seams of a serpentinous mineral, 

 and passes frequently into granite, quartzite, felsite, and a fine- 

 grained porphyry, with interspaced flakes of hornblende, felspar, 

 and mica. 



In the districts of Gabarus and Louisberg felsites predominate, 

 and at the former place include beds of felspathic sandstone. Pos- 

 sibly further examination may assign these rocks to a horizon higher 

 than that represented by the East Bay section (to be given below), 

 or they may prove to be later than the crystalline limestone series. 



At Cape Porcupine, on the Strait of Canso, slates occur with coarse 

 syenite, and felsites resembling those of Louisberg and Gabarus. In 

 the Sporting Mountains the felsites occur with red syenite, whereas 

 the Craignish mountains are composed principally of reddish syenite, 

 overlain by the limestone series. In the northern part of the island 

 the exposures of the great expanse of these rocks present the same 

 general features. It may be assumed that a more minute and extended 

 study must be devoted to this interesting series of measures before 

 it can be decided what subdivisions, if any, can be determined on. 



* The term " syenite " is applied by the Canadian Geological Survey to a 

 mixture of quartz, soda or potash felspar, and hornblende. 



