DRIFT DIVISION. 
195 
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 traversed the wil¬ 
derness to the east-northeast 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 shows that the debris of the present day is nearly stationary. The 
containing shores of this channel are of different formations, one being of limestone and the 
other of greenstone ; each shore is lined with its own debris, and without admixture. A few 
well rolled granites, pudding-stones and an occasional greenstone, do, however, occur among 
the calcareous matter. 
“ In the spring, the ice occasionally removes fragments of great size. During winter it 
surrounds those which are placed in the shallows, and on being broken up in April by the 
mild weather and casual rise of water,* it carries them 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, are deposited rolled stones some yards in diameter, 
with a furrow extending from them to the water, most probably tracing the last steps of the 
route to their place of rest.”! 
It may not be improper to state the results of observations made in Europe and other parts 
of the world, in relation to erratic blocks and boulders. 
It was at the foot of the Western Alps, and principally upon the eastern declivities of the 
Jura mountains which are opposite this great chain, and which are separated by the long and 
broad valley of the Aar, that the first and most curious observations upon the abundance, 
size, and position of these erratic blocks were made. In the small valleys between the cal¬ 
careous crests of the Jura, sixteen hundred feet above the valley, and almost enclosed by 
high walls of rock, large masses of these erratic rocks were found. They are always on the 
surface, or at most embraced in the vegetable soil, or loose sand, but never imbedded in any 
rock. The blocks of each Canton are very similar to each other, but different from those of 
the other Cantons; it is only in the great valley of the Aar that they are mingled. MM. 
Escher and De Buch, by examining with care the predominant nature of the rocks of each 
group of the Alps, by ascending all the valleys, seeking with care the principal bodies from 
which these blocks had been derived, by means of the scratches and furrows they had left on 
the rocks over which they had passed, were enabled to ascertain their sources. They found 
that they must have been derived from the high parts of the mountains, at the heads of the 
valleys which debouched into the basins, on the sides or bottoms of which they were disco¬ 
vered, They saw that these blocks were similar to the fundamental rock of the mountains : 
* This is very commonly observed on the wind’s blowing a few days from the opposite quarter, 
t American Journal of Science, Vol. 3, p. 256. 
