MICHIGAN ACADEMY OF SCIENCE. 
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various regions now low or wholly drowned, rests upon the fact that in 
these several regions land animals and plants and freshwater animals 
are found so distributed that only former connections hospitable to 
them can account for their observed occurrence. In some cases the 
land connections are drowned in the sea. In others, as the freshwater 
forms, the saltness of the water is the feature that renders intercommun- 
ication impossible, in still others the connecting lands have become 
inhospitable not through drowning but by change of climate which is 
best interpreted in terms of altitude. The time of the various connec- 
tions and of their disappearance have been inferred from the palaeontol- 
ogical succession and from the amount of differentiation by which 
groups now separated appear to have diverged since the disappearance 
of the “bridges” over which they were once continuous. For many of 
the extinct bridges this discussion has no place because they belong to 
Mesozoic time. Such, for instance, are those between the now widely 
separated land masses of the southern hemisphere. Still others, notably 
the supposed Tertiary connection between Europe and America via. 
Greenland, are omitted because they are open to question for one reason 
or another and are to be dealt with in a later communication. 
Even with an attempt at caution, some items of evidence have doubt- 
less been included which will be challenged by many, but it is confidently 
hoped that after all crude errors shall have been eliminated there will 
still remain sufficient widely distributed evidence of Pleistocene eleva- 
tion and postglacial depression to form an adequate basis for the critical 
analysis which is attempted. 
BERING BRIDGE. 
It was, I believe. Professor ITuxlev who first suggested a former land 
bridge between Alaska and Siberia to account for the distribution of 
plants and animals. This suggestion, welcomed by I)r. Wallace, has 
been accepted by practically everyone since, and while there are certain 
difficulties with it and it may possibly, later on, be found to have been 
a less important factor than is now thought, it is at the present one 
of the least debatable instances of a land connection, of late Tertiary 
and Pleistocene time, now submerged. While the amount of elevation 
required to obliterate the present Bering Strait is slight, there are not 
lacking indications that in Pleistocene time and earlier there was a high- 
way far enough to the south to accommodate forms which would pre- 
sumably find a cold climate a barrier not to be passed in competition 
with others better adapted. The Bering Bridge has therefore been 
widened by some to include the Aleutian Islands; by others they are 
still omitted. 
SANTA BARBARA ISLANDS. 
In connection with the submerged valleys of river erosion and the 
testimony of the present rivers of California, which LeConte, Fairbanks 
and Upliam believe clearly establish the vertical movement of that 
region, we have the authentic record of the finding on the Santa Barbara 
Islands of the bones of extinct Quaternary mammalia, including the 
Mammoth, under circumstances that preclude the possibility of their 
occurrence being adventitious. This fact alone is held to establish the 
former connection of the islands with the mainland. 
