18 



Topography. 



The Port Coldwell region is exceedingly rough and 

 rocky, consisting of high rounded hills scantily covered 

 with soil or drift material, and therefore easy of geological 

 examination. The central part is in general of higher 

 altitude than the remainder, gradually sloping both to the 

 east and west. The highest point is a hill on Pic island 

 which, according to aneroid determination is 850 feet 

 (259 m.) above the lake. In the vicinity of Red Sucker 

 and in the Coldwell peninsula some of the elevations vary 

 from 250 to 700 feet (76 to 213 m) above the lake,* Fires 

 have destroyed most of the forest in the vicinity of the 

 railway. 



GEOLOGY OF THE AREA. 

 General Relationships. 



It is impossible as well as unnecessary to describe in 

 detail the mineralogical composition of all the varieties of 

 these syenites, for as usual their extreme and rapid variation 

 in this respect is one of the most noteworthy features of 

 their development. They are all, however, differentiation 

 products of a highly alkaline magma representing one 

 phase of plutonic intrusion. Although for purposes of 

 description they may be considered as divisible into seven 

 groups, it must be understood that no natural line exists 

 between these respective subdivisions. 



1. Quartz syenite. 



2. Red hornblende syenite. 



3. Augite syenite (laurvikite). 



4. White syenite. 



5. Nepheline syenite. 



6. Essexite, olivine gabbro and picrite. 



7. Camptonite. 



Petrographic Descriptions of Chief Types. 



Quartz syenite. — Quartz syenite is perhaps the least 

 important of these groups, for it is a comparatively rare 



* The mean water level of Lake Superior (1871-1900) was 601 .7 feet (183.38 m.) 

 above mean tide level. 



