Upham.] 
170 
[May 21, 
bluffs at Decorah, Iowa; the similar occurrence of white pines at 
many localities on river-bluffs in southeastern Minnesota, many 
miles southwest of the ordinary limits of this species ; of the May- 
flower (Epigaea repens, L.) at Plainview, Minn. ; of Scolochloa fes- 
tucacea, Link, in Emmet county, Iowa ; and of Achillea multiflora’ 
Hook., on the Pembina and Park rivers, North Dakota. All these 
are readily accounted for as remnants of the Arctic and boreal flora 
which was forced to migrate alternately southward and northward 
by the climatic changes of the glacial and postglacial epochs. 
Countries bordering the North Atlantic have experienced gener- 
ally warmer temperatures than now, both of the sea itself and of 
the air and winds upon the land, for a considerable time since the 
Glacial period, apparently extending, but probably in diminishing 
degree, nearly to our own day. On the coast of New England and 
the Eastern Provinces, colonies of southern species of marine 
mollusks are found in Casco and Quohog bays, Maine, and even in 
the southern part of the Gulf of Saint Lawrence, such as are com- 
mon along the warmer shores south of Cape Cod, but whose con- 
tinuous range does not pass north of Massachusetts. These isolated 
southern species include the oyster (Ostrea Virginiana, Lister), 
quohog (Venus mercenaria, L.), Pecten irradians, Lam., Ilyanassa 
obsoleta, Stimpson, Urosalpinx cinerea, Stimpson, and others. 
Professor Verrill believes that they are “survivors from a time when 
the marine climate of the whole coast, from Cape Cod to Nova Sco- 
tia and the Bay of Fundy, was warmer than at present, and these 
species had a continuous range from southern New England to the 
Gulf of Saint Lawrence.” Furthermore, we have to note that oys- 
ter and quohog shells are found in abundance in the Indian shell- 
heaps on the coast of northeastern Massachusetts and on islands 
in Casco bay, Maine, where they are thus known to have flourished 
in very recent times, though now they are rare or extinct in the 
same localities. 
A few southern plants also survive from this warmer period on 
or near our northern Atlantic coast, as the Magnolia glauca, L., 
which grows on Cape Ann, but not elsewhere north of the vicinity 
of New York City, and Rhododendron maximum, L., which occurs 
rarely. in damp woods, somewhat inland, from Nova Scotia to Lake 
Erie, but it is very common through the Alleghanies in the South- 
ern States. Even northward to Greenland evidences of such a 
warmer postglacial climate are found, and an increase of cold seems 
