Upham.] 
310 
[Nov. 4, 
depth slightly below the lowest tide, and each also has other 
species that are chiefly restricted to the shore above low water 
mark. Probably the best interpretation is that suggested by the 
layer of peat at the first locality, immediately overlying the 
fossils, near the low tide level. The water there was gradually 
becoming shallower, and the land was finally lifted above the 
reach of the tide at the time of formation of the peat. Subse- 
quently it has been depressed at least several feet, which latest 
movement has now apparently ceased on this part of the coast. 
Postglacial oscillations of considerable amount, thus lifting the 
land and afterwards depressing it, are known to have affected a 
large part of our Atlantic seaboard ; and Professor A. E. Verrill 1 
and Sir William Dawson 2 believe that these recent changes of 
level have been sufficient to explain the important changes of tem- 
perature of the sea here, whereby southern mollusks were per- 
mitted to extend northward to the Gulf of St. Lawrence but have 
since been exterminated, excepting isolated colonies, north of 
Cape Cod and Massachusetts Bay. Both these authors are in- 
clined to attribute the northward extension of the southern fauna 
to a recent time of greater elevation of our coast, which is abun- 
dantly attested to a certain amount, varying from ten to at least 
forty feet, 3 by stumps of forests, rooted where they grew, and by 
peat bogs, now found submerged by the sea at many places along 
all the distance from New Jersey to Newfoundland. Professor 
Verrill suggests that the strait of Belle Isle, which is about ten 
miles wide and 180 feet deep in its narrowest and shallowest part, 
may have been closed by the elevation, shutting out the cold 
waters that pour through it, carrying small icebergs and floes into 
the Gulf of St. Lawrence ; while as great an uplift of the exten- 
sive shallow Fishing Banks would ward off the Arctic current far 
into the ocean. If we had to consider this coast alone, the ex- 
planation would seem very acceptable ; but evidences of such 
warmer postglacial temperature, both of sea and land, succeeded 
1 Am. Jour. Science, III, vol. vii, pp. 134-8, Feb., 1874. 
2 Acadian Geology, Third edition, with supplement, 1878. 
3 According to Sir William Dawson, 1. c., p. 31. Since'this paper was prepared, the 
author finds that Mr. Robert Chalmers reports a peat bed under the Tantramar salt 
marsh at the head of the Bay of Fundy, about eighty feet below the present high tide 
level (Annual Report of the Geological and Natural History Survey of Canada, new 
series , vol. iv, for 1888-89, pp. 42 A and ION), 
