GEOLOGY. 



ON THE GEOLOGY OF EXTREME NORTHERN AMERICA. 



AT a recent meeting of the London Geological Society, Mr. Isbister presented 

 a paper on the geological features of the extreme northern portions of America. 

 In respect to the Rocky Mountains, he stated that granite, limestone, and 

 slate (probably of Silurian age), and conglomerate and sandstone, have been 

 met with on their eastern slopes. Rocks probably referable to the Carbonif- 

 erous series, have been found by the author near the northern extremity of 

 the range. The Lawrentine Mountains, or the range flanking the north bank 

 of the St. Lawrence, also consist of granite, with other crystalline rocks. 

 These are prolonged (with a narrow slip of palasozoic rocks intervening) in a 

 N.~W. direction, from Lake Superior to the Arctic Sea, in a broad zone of but 

 slight general elevation. It is crossed by numerous rivers, and greatly inter- 

 sected by lakes ; indeed, along its western margin nearly all the great lakes 

 of North America occur. Between this range and Hudson's Bay is the great 

 Silurian basin of Hudson's Bay, which extends also along the northern margin 

 of the Lawrentine Mountains. The shores of the Bay itself are flat and allu- 

 vial. The Silurian limestone of Hudson's Bay has been traced more or less 

 continuously to the Arctic Sea, through the enormous range of thirty degrees 

 of latitude ; and the fossils obtained from it, both in the North and near Hud- 

 son's Bay, appear to belong exclusively to the Upper Silurian series. The 

 Silurian basin of Lake "Winnipeg was next described. Many fossils have been 

 collected, but some obscurity still exists with regard to the age of the rocks 

 of this tract ; in some respects they appear to be referable to the Lower 

 Silurian age. The valley of the Mackenzie River is chiefly occupied by rocks 

 of Devonian age, in which sandstones alternate with bituminous shales, some- 

 times to a depth of 150 feet. In the Mackenzie Valley there are also rocks 

 referable to the Silurian, and some which the author refers with doubt to the 

 Carboniferous series. The latter include 1st, the great alum-shale deposits 

 occurring along the Arctic coast from Mackenzie River to Liverpool Bay ; 

 2d, the extensive band of lignite and coal, described by Sir J. Richardson, 

 from whose account it appears that a vast coal-field skirts the eastern base of 

 the Rocky Mountains, and is apparently continued far into the Arctic Sea, 

 where coal has lately been met with by Captain M'Clure. In the drift-coal 

 of Jameson's Land and of Melville Island, and in the coal-fields of Oregon, 

 plants like those of the English coal measures have been found. The author 



