1908]  Sears,— A southern Flora in Essex County, Mass. 45 
etc., were used by the Indians as food, they must have lived here in 
our tidal estuaries and harbors until modern times. 
ІП. Тһе warm epoch along the coast of Essex County and north- 
em New England is explained by an elevation of the land in New 
England and adjacent regions which followed the Champlain sub- 
sidence. At the end of the Champlain subsidence the land on our 
coast had become submerged to a depth of 360 or more feet, as pointed 
out in the Physical Geography and Geology of Essex County.! After 
the Champlain subsidence the land was again elevated, as is proved 
by the finding of fossil shells of Portlandia arctica Gray, P. lucida 
Loven, and other species of Arctic mollusks, together with the hard 
parts of a large starfish, Asteracanthion Lincki Muhler, in the clay 
beds at about the present sea level їп Danvers and Lynn, Essex 
County, Massachusetts; for at present the above species of Portlandia 
are taken alive on the coast of Norway only at a depth of from 360 to 
500 feet. Judging from the rate of the subsidence now going on? 
about one foot in a century, this elevation of 360 or more feet must 
have taken approximately 36,000 years. In the course of this eleva- 
tion at the North, the Straits of Belle Isle must have become land 
locked,? thus forcing the Labrador current, with its cold waters and 
icebergs, to join the Greenland current in its northward flow. This 
closing of the Straits of Belle Isle allowed the warm waters of the 
southern seas to come into Cape Cod and Boston Bays. Under such 
conditions the climate of Essex County and northern New England 
must have been similar to the climate of southern New England, and 
probably to that of the New Jersey coast; and a warm epoch con- 
tinued here probably for a long time. During this epoch the fauna 
previously described, of Ostrea, Pecten, etc., was introduced and 
multiplied in our waters; and as the land emerged above the waters 
the southern flora took possession of it. Some of the plants of that 
southern flora, as previously noted, have survived to the present time, 
according to situation or environment, and have become acclimated. 
Professor James D. Dana writes “Оп the coast of Maine there are 
large Indian shell heaps of the common clam, Venus mercenaria (the 
Quahog of the Indians) and, in some places, of the Virginia Oyster, 
species that are now nearly extinct on the cold coast. Аз made known 
by Verrill there is a colony of living southern species in Quahog Bay, 
1 Sears, Phys. Geogr., Geol. etc. of Essex Co. 373. (1905). 
? See Sears, l. c.; Chapter on Subsidence, p. 58. А 
3 At the present time an elevation of 200 feet would close the Straits of Belle Isle, 
