Dr. BiGSBY on the Geography/ and Geology of Lake Huron. 189 



very near the main ; but further out in the lake they are loftier^ and sometimes 

 girded with a belt of flat ground^ richly wooded. This belt was in many 

 instances visibly supported on an horizontal dark slaty rock, which afterwards 

 proved to be shell limestone. The primitive rocks of these islands retained 

 their wonted sterility. Both the islands themselves, and most of the ridges of 

 which they are composed, have a south-west direction ; and individual masses 

 of gneiss were observed to dip either vertically or more or less to the south- 

 east; — a coincidence in position with the gneiss of the whole valley of the St. 

 Lawrence, worthy of being remarked. 



The Isles of La Cloche form a charming contrast to the bleak hills of the 

 main, in their forests and grassy vales, diversified, like an English park, by 

 clumps of fine trees. Some of them are composed, as I am informed (for I did 

 not see it), of a dark rock, which when struck sounds like a bell. 



From La Cloche to the river Missassaga, a distance of 60 miles, is another 

 assemblage of isles ; but principally, I believe, within 6 miles of the shore. 

 In the first five leagues from La Cloche, they are woody, except those near 

 the shore, which are barren, and composed of gneiss. Landing here on the 

 main, I found issuing from a morass a round smooth mass (probably a vein), 

 50 yards broad, of cr3'stalline quartz rock, running south-west, and containing 

 nests of silvery mica and galena. The former in some parts combining with 

 the rock, rendered it fibrous. 



Twenty miles from La Cloche, and four from the main, is a chain of five 

 or more short islets, parallel to each other, and having their long diameter to 

 the north. They are composed of genuine granite ; and are bare, low, and 

 smooth. 



Further to the west, soon after this, a multitude of small sterile islets, loaded 

 with debris, occur for 20 miles along the shore, composed chiefly of horn- 

 blende rock. They are of a deep black colour, and in one instance had the 

 glazed lustre occasional in this mineral. The rock varies in its constituents. 

 On the east it is moderately pure, but seldom very crystalline. Further west, 

 it takes a green tinge, and in certain spots feldspar or quartz is visible in 

 grains. It is often traversed by beautiful and strong veins of quartz, clouded 

 green and red. The compact black species contains much olivine, and some 

 elongated crystals of hornblende. 



From hence to the river Missassaga, another appearance is noticed. The 

 islets of granite return, intermingling with the trap, both rocks being in the 

 form of low oblong smooth mounds ; the granite taking a northerly direction, 

 and the trap running south-west. Some of the islets possessed the calcareous 

 girdle before mentioned. 



