+? 
28 oe | Erratic Phenomena about Lake Superior. 
Secniealemins “have ‘iin accumulated, not only under different cite 
cumstances, but during long-continued subsequent distinct peri z 
ods, and that great changes have taken place since their deposi- ~ 
tion, before the present state of things was fully established. 
To the first period,—the ice period, as I have called it,—belong. 
all the phenomena connected with the transportation of erratie 
boulders, the polishing, scratching and furrowing of the rocks: | 
and the accumulation of unstratified, scratched, and loamy drift 
During that period, the main land seems to have been, to some 
‘extent at least, higher above the level of the sea than now; # 
we observe, on the shores of Great Britain, Norway and Sweden he 
well as the eastern shores of North America the eae sur- 
a dipping gnder the level of the ocean, which encroaches 
everywhere up@n the erratics proper, ss el the polished eae 
and remodels the glacial drift. During these periods, large ter- 
restrial animals lived upor®both continents, the fossil remains of 
which are found in the drift of Siberia, as ‘well as of this conti- 
nent. A fossil elephant recently discovered in Vermont* adds to 
the resemblance, already pointed out, between the northern drift 
of Europe and that of North Ametica ; for fossils of that genus 
are now known to occur upon the northernmost point of the west- 
ern extremity of. North America, in New England, in Northern — 
Europe, as well as all over Siberia. 
To the second period we would refer the stratified devas 
resting upon drift, which indicate that during their deposition the 
pasties eon ape had again extensively subsided under the sur- 
ace o 
During this Boi animals, identical with those which occur 
in the northern seas, spread widely over parts of the globe which 
are now again above the level of the ocean. But, as this last 
elevation seems to have been gradual, and is even still going on 
in our day, there is no possibility of tracing more precisely, at 
least for the present, the limit between that epoch and the present 
state of things. ‘Their continuity seems almost demonstrated by 
the identity of fossil shells found in these stratified deposits, with 
those now living along the present shores of the same continent, 
and by the fact “that changes in the relative level between sea 
and main land are still going on in our day. 
Indications of such relative changes between the level of the 
waters and the land are also observed about Lake Superior. And 
here they assume a very peculiar character, as the level of the 
lake itself, in its relation to its shores, is extensively changed. 
All around Lake Superior we observe terraces at different lev- 
els ; and these terraces vary in height, from a few feet above the 
present level of the lake, to several hundred feet above its surface, 
+ ee ih doemnad;-sid ie’: 
