Dr. BiGSBY on the Geography and Geology of Lake Huron. 207 



contained within its fissures. In the spring the nocturnal frosts and diurnal 

 thaws are very violent. In the winter the thermometer is frequently 50° below 

 the freezing point, and in summer it ranges from 60° to 90° of Fahrenheit. 

 I once saw it at noon, on the 20th of June, 1820, at 101^° in the shade. 



These recent fragments, whether of the older or newer rocks, are angular 

 and mostly small, and cover their parent rocks, as well in the high as in the low 

 grounds, often to the depth of several feet. Examples of this are seen in the 

 slaty greenstone of the Narrows, in the quartzose limestone of Drummond, 

 and in the quartz rock at the foot of Lake George. — All the countries to the 

 north of Lake Huron are loaded with similar debris. The French river, in 

 one wild spot, the scene of an Indian massacre, is almost choked with it. In 

 Lake Nipissing, near its southern shore, there is a large heap of square clean 

 masses of gneiss piled together promiscuously. 



An instructive fact is presented by many parts of Lake Huron, and very 

 strikingly in the channels of Pelletau. It shows that the recent debris is nearly 

 stationary. The opposite shores of this channel consist of different rocks, 

 the one being limestone, the other greenstone. Each shore is lined with its 

 own debris, without any admixture, except that of rolled pebbles of granite, 

 pudding-stone, or greenstone, left by the debacle on the calcareous beach. 



In the spring the ice occasionally removes fragments of great size : the in- 

 habitants of Quebec annually see them transported in this manner down the 

 St. Lawrence. During the winter the ice surrounds the blocks that are upon 

 the shallows ; and on being broken up in May, it carries them by a rise of 

 water to some 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 a little above its level, rolled stones, many feet in diameter, are found de- 

 posited, with a furrow extending from the water to their present place of rest. 



That changes in the level of Lake Huron have occurred, and that its surface 

 once stood much higher than at present, is proved by the traces of ancient 

 beaches and zones of rolled stones and sand that are found in the neighbour- 

 hood of the lake. Such an occurrence has been noticed in Collier's Harbour, 

 at Blockhouse Hill, which has the appearance of a beach, and of having formed 

 the west end of the Isle of Drummond, when the lake stood higher than at 

 present. Similar alluvial ridges are found surrounding the other lakes and 

 rivers in Canada. These may be accounted for partially by the effects of the 

 wind ; which, blowing strongly from certain quarters for a few days, accumu- 

 lates the water on the leeward coast, the waves there washing up the shingle 

 in scalar ridges to the height of 6, 8, or 10 feet. 



On concluding this Memoir, I have to express my grateful acknowledge- 



VOL. VI. 2 E 



