254 Geology and Mineralogy of the 



Art. VI. — Geological and Mineralogical Observations on 

 the North West Portion of Lake Huron ; by Dr. John 

 I. Big SB Y, of the Medical Staff of the British army in 

 Canada, and Assistant Secretary under the 6th and 1th 

 Articles of the Treaty of Ghent. 



TO THE EDITOR OP THE AMERICAN JOURNAL OP SCIENCE. 



Sir, 



I VERY respectfully beg your acceptance of a few geolo- 

 gical observations on the north west portion of Lake Huron ; 

 collected under rather favorable circumstances in the sum- 

 mer of 1820. 



The part of Lake Huron under examination is contained 

 within the Latitudes 45° 46' and 46° 20' ; and by the Lon- 

 gitudes 83° and 84°, with some exceptions of small im- 

 portance. 



At the upper part of this space the waters of Lake Supe- 

 rior are received, through the medium of the straits of St. 

 Mary and the minor Lake, George ; and by three channels, 

 the sum of whose breadth perhaps does not exceed a mile — 

 as the interval of three leagues or more between the north 

 and south shores of Lake Huron, is here (Ion. 84° lat. 46° 

 20') principally occupied by the large islands of La Crosse 

 and St. Joseph. 



St. Joseph, with which we are more immediately con- 

 cerned, is compact in shape and woody, rising to the height 

 of five hundred feet in the centre. It is about sixty-five 

 miles in circumference. Its most southern point is at Fort 

 St. Joseph, in the latitude of 46° 5' — six miles north of 

 Drummond Island. 



This latter island is the most western of the great Mani- 

 touline chain ; which in the latitude of 45° 58', divides the 

 Lake into two unequal parts. One extremity approaches 

 to within a mile of the South Main, in Ion. 83° 52', and the 

 other is contiguous to Cabot's Head. 



Drumraond's Island is an assemblage of rocks and mo- 

 rasses, seventeen to twenty miles long, by five in average 

 breadth. 



The lesser Manitou, which next presents itself in the linCj 

 is of a similar character, and is about seven miles in diameter 



