206 W. Upham — Recent Fossils near Boston. 



the St. Lawrence valley opposite the Saguenay, and 520 feet 

 at Montreal ; 300 to 400 feet, increasing from south to north, 

 in the basin of Lake Champlain; about 275 feet at Ogdens- 

 burgh, and 450 feet near the city of Ottawa; 300 to 500 feet 

 on the country southwest of James Bay ; in Labrador increas- 

 ing 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 being melted 

 away, is proved by the occurrence of fossil shells of Lecla 

 aretica 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 

 depression 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 is 

 included, excepting perhaps the oyster in southwestern Maine.* 

 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 by 

 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 remarked, that the warmer marine tempera- 

 ture 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 north- 

 western 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-eleva- 

 tion brought the land up to its present height. After this- 

 level was generally attained or somewhat surpassed, the south- 

 ern warmer temperate species spread northward along both 

 sides of the Atlantic to boreal and even Arctic regions, where' 



•0. 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 

 Labrador 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). 



