Upham.J 
312 
[Nov. 4, 
near the city of Ottawa ; 300 to 500 feet in the country southwest 
of James Bay ; in Labrador increasing northward to 1,500 feet at 
Nachvak, according to Dr. Robert Bell ; and in northern Greenland 
and Grinnell Land, from 1,000 to 2,000 feet. That the land 
northward from Boston was so much lower while the ice-sheet was 
melting away, is proved by the occurrence of fossil shells of 
Leda arctica Gray, which is now found living only in Arctic seas 
where they receive muddy streams from existing glaciers and 
from the Greenland ice-sheet. This species is plentiful in the 
stratified clays resting on the till in the St. Lawrence valley, in 
New Brunswick, and Maine, extending south to Portsmouth, 
N. H. But it is known that the land was elevated from this de- 
pression to about its present height before the sea here became 
warm and the southern mollusks migrated along this coast to the 
Gulf of St. Lawrence ; for in the extensive lists of the fossil fauna 
of these beds none of the southern species are included, excepting 
perhaps the oyster in southwestern Maine. 1 
From the Champlain submergence attending the departure of 
the ice, the land was raised somewhat higher than now, and its 
latest movement from New Jersey to southern Greenland has 
been a moderate depression. The vertical amount of this recent 
subsidence is undetermined, beyond that known b}^ stumps and 
peat now covered by the sea ; and it is difficult to estimate how 
far this recent and probably slight oscillation may have tended to 
produce formerly warmer and now cold sea currents, with the 
faunal migration that is represented by the marine colonies of 
southern species. It seems unlikely, however, as before re- 
marked, that the warmer marine temperature was due to local 
conditions of our coast, since it prevailed throughout all the 
North Atlantic Ocean. The fossils of the Champlain beds of our 
northeastern shores and also of northwestern Europe show a 
gradual change from an Arctic and glacial climate at the maximum 
of the depression to a cool temperate climate, nearly the same as 
now, before the re-elevation brought the land up to its present 
height. After this level was generally attained or somewhat sur- 
1 C. H. Hitchcock, “The Geology of Portland,’’ Proc. A. A. A. S., vol. xxii, for 
1873, pp. 163—175. A. S. Packard, “Observations on the Glacial Phenomena of Lab- 
rador and Maine,’’ Memoirs of the Boston Society of Natural History, vol. i, 1865, pp. 
210-262. J. W. Dawson, Notes on the Post-pliocene Geology of Canada, 1872, pp. 112 
(from the Canadian Naturalist, new series, vol. vi). 
