MICHIGAN ACADEMY OF SCIENCE. 
120 
strip of lowland surrounding the main, which afforded satisfactory 
climatic conditions to the forms driven down from the heights. The 
same would be true in the tropics, even though glaciation did not super- 
vene. If, as according to Darwin’s view, the isotherms were shifted 
down, or the land up. amounting to about the same thing, to the extent 
of only about 5,000 or 6,000 feet, which would permit the growth of 
a mixed temperate and tropical flora, there would presumably slid 
remain heat-loving forms that would need still lower levels with greater 
warmth for their survival in the struggle for existence, so that in the 
tropics as well as in the northern climes there is need for low and warm 
borders to the continents coexistent with the general elevation. Refuges 
may be needed not only from glacial cold but from relative cold. 
EAST INDIES. 
Sumatra, Java, Borneo and the Malay Peninsula are separated by 
shallow seas. Their plants and animals are almost as closely related 
as if they were still connected.* Xever-the-less there are not lacking- 
many specialized forms which are restricted to particular islands and 
which argue for a reasonable lapse of time since the connections were 
inundated. If we view these islands in the light of much external evi- 
dence we find nothing which need oppose the theory that their (relative) 
depression dates as far back as the end of the Glacial Epoch. 
Dr. Wallace treats the lowering of these islands as a purely local 
problem and thinks that it was caused by the extrusion of lava from 
under the earth’s crust. There are several objections to this theory but 
they do not demand discussion here. We may say that this is only 
one instance among similar ones of the drowning of land connections 
all over the world and that this drowning is, like all the rest, related 
to the submerged borders of all the continents and is to be treated 
not as a purely local problem but in its proper relations. 
MID-PACIFIC. 
Upon the map, Figure 5, one more region of drowning remains to be 
touched upon. Pilsbryf found the freshwater and land mollusca of the 
mid-pacific islands sufficiently closely related to force the conclusion 
that they have been elaborated in areas much greater than they now 
possess and that their habitats were continent. But this is nothing new. 
it has been argued for years that the Pacific islands are only the peaks 
of extensive regions formerly land and now drowned. If the molluscan 
relationships went back as far as the Mesozoic we might have to pass 
the region by in the present connection but they are said to be much 
more on the order of the late Tertiary and early Quaternary, at least 
between the various islands of particular groups. In general it is a 
development from primitive groups which cannot be traced to conti- 
nental affinity later than the Mesozoic . % 
There are a number of problems in (lie Pacific whose solution seems 
* Wallace, Alfred It. , “Malay Archipelago,” 1869. 
fPilsbry, H. A., “The Genesis of Mid-Pacific Faunas.” Proc. Acad. Nat. Sci., Phila. 1900, pp. 
568-581. 
JThis paragraph is unsatisfactory to the writer and yet there seem to bp reasons for leaving if as 
it is. Comment is cordially invited. 
17 
