southern marine mollusks are known. With the subsequent de- 
crease of the size of Bering Strait, during the past 1,000 years, 
sending more of the Japan current to our Pacific coast, the Cor- 
dilleran and Alaskan glaciers would be melted away or greatly 
reduced, as to-day, but Greenland and the North Atlantic area 
would become colder, as seems to be well proved within the pres- 
ent historic period. 
To the same very late date we must assign the extinction of 
the southern molluscan species on the eastern coast of New 
England and the southern coast of New Brunswick and Nova 
Scotia. During the time of accumulation of the aboriginal shell- 
heaps or kjokken-raoddings of Maine, and even within the 270 
ygars since the first settlement in Massachusetts, very significant 
restriction and extinction can be shown. For example, Professor 
Verrill states that dredging reveals the occurrence of great beds 
of oyster shells a few feet beneath the harbor mud at Portland, 
where they are associated with the quahog ( Venus mercenaria ), 
scallop ( Pecten ir radians ) , and other southern species; and that 
the oysters and scallops “had apparently become extinct in the 
vicinity of Portland harbor before the period of the Indian shell- 
heaps, for neither of these species occurs in the heaps on the ad- 
jacent islands, while the quahogs lingered on until that time, but 
have subsequently died out everywhere in this region, except at 
Quahog Bay.” 1 Still later and more surprising is the extinction 
of the oyster from many localities on the coast of Maine and east- 
ern Massachusetts. 2 Native oyster banks in the Charles and Mys- 
tic rivers two hundred years ago were so productive that an 
enumeration of the exports from Boston to the West Indies and 
Spain in 1687 included “oysters salted in barrels, great quanti- 
ties of which are taken here.” Now there probably remain, ac- 
cording to Ingersoll, only two localities on the New England 
coast north of Cape Cod, where native oysters survive, these be- 
ing Great Bay in New Hampshire, back of Portsmouth, and the 
Sheepscot river in Maine. They are likewise almost wholly 
wanting on the Canadian continuation of the coast until Cape 
Breton Island is reached ; but thence westward in the Gulf of St. 
1 Am. Jour. Science, III, vol. vii, p. 137. 
2 Ernest Ingersoll, Report on the Oyster-Jndustry of the United States, Tenth Cen* 
gus, 1881. 
