256 Geology and Mineralogy of the 



These fragments are incredibly numerous in Lake Hu- 

 ron, and may be divided into two geological classes, the for- 

 eign and the native. The former are the more plentiful, 

 and are round and smooth. They are seen every where 

 but are collected principally in the interior of the coasts and 

 islands either in confused heaps, or in parallel ridges, and 

 crowning the highest acclivities in great numbers and the frag- 

 ments are of various dimensions. They belong almost exclu- 

 sively to the older orders of rocks, and are therefore of a 

 northerly origin. Granites, gneiss, mica slate, and porphyries 

 prevail, of kinds which I never saw in situ, although I have 

 skirted the north shore for two hundred miles, and have trav- 

 ersed the wilderness to the east north east for six hundred 

 miles. Mica slate I never met with in a fixed state, excepting 

 a few strata of the black variety at the Falls des Chat, on the 

 Ottawa. 



The other class is small, angular and ragged. They are 

 most frequent on the beaches, whither they are driven by 

 the waves. 



A curious fact is presented by many parts of Lake Huron, 

 and very strikingly in the north channel to St. Mary's. It 

 shews that the debris of the present day is nearly stationary. 

 The containing shores of this channel are of diiferent forma- 

 tions, the one being of limestone and the other of green- 

 stone ; each shore is hned with its own debris, and without 

 admixture. A few well rolled granites, puddingstones and 

 an occasional greenstone do however occur among the cal- 

 careous matter. 



In the spring the ice occasionally removes fragments of 

 great size. During the winter it surrounds those which are 

 placed in the shallows, and on being broken up in April by 

 mild weather, and a casual rise of water,* it carries them to 

 ^ome other shore. Remarkable instances of this are found 

 on the islets near the south end of St. Joseph, where a few 

 yards from the water and little above its level, are deposit- 

 ed rolled stones some yards in diameter, with a furrow ex- 

 tending from them to the water, most probably tracing the 

 last steps of the route to their place of rest. 



Changes in the form of the bed of the lake indicate very 

 strongly changes also in the nature and quantity of its water. 



* This is very commonly observed on the wind's blowing a few days from 

 the opposite quarter. 



