178 THE CANADIAN NATURALIST. [May 



throw some Light on their origin and age, I have attempted to 

 describe them in the following paper. 



Four different formations are distinguishable on the north, south 

 and east shores of the Lake, where I have had an opportunity 

 of examining their constituent rocks and mutual relations, but the 

 same formations may be observed elsewhere in this region. These 

 formations have been designated as follows: The Laurentian 

 system, the Huronian series, the Upper copper bearing rocks of 

 Lake Superior and the St. Mary sandstones. The two first- 

 named (and older) formations usually occupy those parts of the 

 shores which form high promontories and precipitous cliffs, and 

 they constitute, almost exclusively, the areas which have been 

 explored in the interior. On the other hand, the Upper rocks 

 and St. Mary sandstones are never found far inland, but occur 

 close to the shore in comparatively low-lying land and rocks. 

 They seem to have had, as the theatre of their eruption and 

 deposition, the bottom of the Lake, at a time when its surface was 

 at a higher level than it is at present, although not so high as the 

 general surface of the surrounding Laurentian and Huronian hills. 



I. — THE LAURENTIAN SYSTEM. 



Under this name it has become usual, in Canada, to class those 

 rocks which, in other countries, have been regarded as forming 

 part of the primitive gneiss formation, of the primary or azoic 

 rocks, or of certain granitic formations. 



The most prevalent rocks of the Laurentian series on Lake 

 Superior present a massive crystalline character, partaking much 

 more of a granitic than of a gneissic nature. Some of these I shall 

 endeavour to describe first. To the north of the east end of 

 Michipicoten Island, on the mainland, there is a very large area 

 of reddish-coloured granite, which exhibits, in a marked degree, 

 the phenomena of divisional planes, and huge detached blocks. 

 The rock is coarsely granular, has a specific gravity of 2-668 to 

 'J-676, and consists of reddish o.'thoclase, a small quantity of 

 a triclinic felspar, dark green mica (also in small quantity), and 

 greyish white quartz. The mica is accompanied by a little 

 epidote, and an occasional crystal of spheue may be detected. A 

 ew miles to the east of Dog River a grey granite occurs exten- 

 sively, which does not show any divisional planes. The felspar of 

 this variety is yellowish white, with dull fracture, and is fusible 

 without difficulty. It is associated with black, easily fusible 

 mica, in considerable quantity, and with quartz, which is occa- 



