352 THE VERMILION IRON-BEARING DISTRICT. 



a^jpearing at the water level a couglomeratic looking rock, the pebbles of 

 which seem to be a dense quartzitic graywacke or slate, whereas the 

 matrix is light colored, rather coarse grained, and appears like an exceed- 

 ingly feldspathic biotite-gabbro. This conglomeratic rock is cut by a sheet 

 of basalt 12 to 16 inches wide, which is very nearly horizontal, showing- 

 only very slight east-west rolls. The basalt sheet is separated into 

 very symmetrical hexagonal columns, and shows a distinct fine basalt 

 selvage, while at its center the sheet is coarser grained. Ascending the cliff, 

 above this conglomeratic rock, we pass from it into a coarse brown, more 

 or less friable rock, which calls to mind Winchell's muscovado. Still higher 

 up this rock is found to grade vertically into a coarse normal gabbrq. This 

 conglomeratic-looking rock continues along the shore still farther to the 

 southwest. 



Following the shore of Gobbemichigamma Lake to the east of our 

 starting point at the cliff, a pseudo-conglomeratic rock similar to that 

 described above begins on the shore just a little north of the meander 

 corner of the town line between Ts. 64 and 65 N., R. 5 W. The rock here 

 is ra.ther fine-grained granular rock, weathering white to yellow and brown, 

 in which occur very frequent rounded areas all essentially alike and 

 seemingly of one kind of rock — a dense, green, fine-grained very quartzose 

 graywacke. A similar rock is well exposed on the little island just west 

 of the shore on whicli the meander corner stands, and here also its relations 

 to the gabbro and its true characters are better shown than elsewhere. 

 The occurrence observed here has already been described (p. 343). The 

 gabbro is evidently younger than the pseudo-conglomeratic rock, which 

 has, in fact, been produced from preexisting sedimentary rocks by the 

 intrusion into them and extensive metamorphism of them by the gabbro. 



SECTION IL— ACID AND BASIC INTRUSIVES OF THE LOWER HURONIAN. 



USTTEODUCTION. 



In Section III of Chapter III various acid intrusives which are of the 

 same general petrographic character and geologic age are discussed. In 

 addition to these intrusives, there are found in the Vermilion district 

 three other large masses of granite and granite-porphyry, from which 

 numerous dikes have been given off. These large masses and accompanpng 



