BLOCKS DRIFTED FROM THE NORTH TO LAKE HURON. 215 
DILUVIAL ACTION IN NORTH AMERICA. 
Dr. Bigsby, in his Memoir on the Geography and Geology of Lake 
Huron, which is about to appear in the 2d part of the first volume of 
the new series of the Geological Transactions of London, has traced in 
America the similar action of a violent flood of waters rushing also from 
the north, and drifting from thence blocks of various primitive rocks 
over the secondary and transition formations that compose the basin 
of that lake. He also notices in this same district, effects similar to 
the diluvial denudations in Europe, in the excavation of valleys, the 
separation of islands from the mainland, the formation of crags and 
serrated ridges of rocks, and the wearing away of the highest 
summits; and shows that these cannot be attributed to any causes 
now in action, or to any gradual subsidence of the waters of the 
lake, but must be referred to the great debacle of a flood advancing 
from the north. The same waters, he adds, have accumulated 
immense deposits of sand and gravel, in heaps and ridges, at various 
levels of the main shores and islands in the lake. These travelled 
fragments are foreign to the district they pervade, and are almost 
exclusively of the older class of rocks; granite, gneiss, mica slate, 
greenstone, porphyry, sienite, and amygdaloids, which occur not in 
the neighbourhood, but may be shown to have come from the north, 
