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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 1 6, 



isles ; but when we come to the south-east angle of this lake, these rocks 

 (granite and gneiss being substituted for mica-slate) over an irregular 

 space of about 300 square miles are so mutually involved and inter- 

 penetrated, and so intimately mixed up together, that it is impossible 

 to give any but the most general account of their disposition, how- 

 ever plainly seen and carefully observed on the spot. In some places 

 (Portage Mouille, &c.) they are in narrow interleavings of no con- 

 stant direction. In another (around Broken Road River) the granite, 

 for large spaces, traverses dark greenstone in a thousand tortuous 

 masses, tongues, and slender veins. 



Fig. 2. — Sketch of a broken fragment of Greenstone (18 inches hy 

 8) in Greenstone-conglomerate at Portage des Bois. 



Veins of granite and quartz, and shapeless or lenticular masses of 

 hornblende, rendered impure by a fine admixture of white quartz, 

 are abundant in all these rocks ; but as such appearances are common 

 elsewhere, they are not here noticed in detail. Two veins of epidotic 

 trap in granite, met with in an island near Portage Mouille, were so 

 artificial in appearance that I sketched them. One of these is re- 

 presented by fig. 3. The isolated needle of trap in fig. 3 is per- 

 haps connected with the contiguous vein of that rock. 



Fig. 3. — Ground-plan of a portion of a Trap-vein in Granite near 

 Portage Mouille. 



Length 10 yards. 



At other places (Turtle Portage, &c.) the whole country within 

 view consists of massive trap. 



Precisely the same appearances may be seen in Lake Superior near 

 Gros Cap, and in Lake Huron between the Rivers Thessalon and 

 Missisaga. These foldings and irregularities seem to be the result 

 of external force. 



