558 APPENDIX. 



The specimens and information obtained by Captain 

 Back, in that part of his route which preceded his own 

 discoveries, accord with the previous descriptions of 

 Dr. Richardson ; and as the places referred to can be 

 but seldom visited, I shall subjoin a general list of 

 the specimens. Among the most remarkable are several 

 fragments of a white or cream-coloured limestone from 

 the north-western extremity of Lake Winipeg, very 

 much resembling a series presented to the Geological 

 Society some years ago (in 1823) by Dr. Bigsby, from 

 the north-western shore of Lake Huron, — a spot more 

 than 600 geographical miles from Lake Winipeg. ^ 



# 



* From Dr. Bigsby's account of the country around Lake 

 Huron, and thence to the south-east, it would appear that 

 the line of division between the primary and secondary 

 rocks, is continued from the neighbourhood of Lake Wini- 

 peg, nearly in the same direction with that above specified, 

 for several hundred miles : — 



" The northern shore of Lake Huron, with its nearest 

 " isles, consists principally of the older rocks ; the secondary 

 " occupy the rest of the lake. The primitive rocks are 

 " part of a vast chain, of which the southern portion, ex- 

 " tending, probably uninterruptedly, from the north and east 

 " of Lake Winipeg, passes thence along to the northern 

 " shores of Lakes Superior, Huron, and Simcoe ; and after 

 " forming the granitic barrier of the Thousand Isles, and 

 i( the outlet of Lake Ontario, spreads itself largely through 

 " the State of New York, and then joins the Alleghanies 

 " and their southern continuations. 



" The secondary rocks of Lake Huron are a portion of an 

 " immense basin, which, extending probably without inter- 

 " ruption, from the southern shore of Lake Winipeg, spreads 

 " itself over the greater part of Lakes Superior, Huron, and 

 " Simcoe — the whole of Lakes Michigan, Erie, and Ontario; 

 " much of the western part of the State of New York, — the 



