254 On the Geography and Geology 



original form, become slightly granular, of red, white, and yellow 

 colours, and even seem stratified horizontally : of the latter fact 

 I should have rendered myself more assured, had my leisure 

 allowed. 



The mineralogical characters of the most common form of this 

 porphyry are nearly the same as of that of Gros Cap. If I had seen 

 more of the latter rock I might have found the varieties existing 

 here. The colours are brick, and brownish red, brown, black, 

 gray, and green, varying in clouds : the lustre of the cement is 

 dull, and the fracture uneven. A gray streak is yielded easily to 

 the knife : but sometimes it is not scratched by steel. A strong 

 earthy smell is emitted on the application of water. In the passage 

 leading from the Nipigon route to Gravel Point the cement is 

 hornblende ; but often containing so much glassy feldspar in large 

 crystals, as nearly to disappear. The imbedded substances are 

 vitreous feldspar in six-sided unequiangular prisms, rectangular 

 and oblique four-sided prisms, usually broken and compressed ; 

 and in size, from microscopic to an inch long. Their colours are 

 opaque white in a dark red base, transparent and colourless in a 

 light red ground, pale red and translucent in a greenish black 

 mass, and transparent yellow on a black base. Every hand spe- 

 cimen contains crystals more or less weathered. They are nu- 

 mferous, but do not often run into each other. This feldspar is 

 almost always accompanied by roundish drops and fragments 

 of transparent crystalline quartz. Green earth and other sub- 

 Stances occur as mentioned above. Lieutenant Bayfield presented 

 me with a group of octahedral crystals of green fluor associated 

 with straight lamellar barytes. He found it in a vein in the por- 

 phyry of the lofty island three miles east from Gravel Point. 



The pale varieties of this rock are extremely full of parallel 

 rents and fissures , but, even after many endeavours I could not 

 ascertain any determinate stratification. The amphibolic species is 

 in very steep, smooth, hummocks. 



From the magnificent headland, Thunder Mountain, greenstone 

 trap predominates to the River St. Louis : my personal examina- 

 tions have only extended to the Grand Portage. 



