94 SEMI-CENTENNIAL OF TORREY BOTANICAL CLUB 
continental or sub-continental area, we can only conjecture. An 
examination of the water areas existing at present (see map 2, 
Century Atlas) shows that between the Islands and North America 
there is an enormous and perfectly continuous area of very deep 
water which extends to the north and to the south of the Islands, 
but leaves an opening on the west which is continuous with a large 
area of less depth comprising pretty much the whole of Polynesia. 
To the southwest are two very large shallow areas including re- 
spectively the Marshall and Caroline Islands, presumably the 
remains of large sunken land masses. А chain of similar but 
smaller shallows extends to the Malay Archipelago, and it is pos- 
sible, at least, that this indicates approximately the line of connec- 
tion between Hawaii and some ancient great southern continent— 
in short, that Polynesia comprises merely the remnants of a larger 
continent, or group of continental islands like Australia. 
As to the period at which Hawaii became completely isolated, 
this of course can only be guessed. It could hardly have been 
earlier than the later Cretaceous or early Tertiary since few of the 
modern Angiosperms existed prior to the upper Cretaceous, so far 
as we know. 
Hillebrand, reasoning from the absence of Conifers, thinks 
that the Islands must have been formed “subsequent to the age in 
which these were universally distributed." It is quite conceivable 
that Conifers may have existed formerly and become extinct as the 
result of the extensive volcanic activities subsequent to the isola- 
tion of the Islands. As the soils of the Islands at present are 
practically exclusively volcanic and are said to be strongly acid, 
this might well account for the absence of many plants which may 
have been found at an earlier period, but which require different 
soil conditions from those now existing. 
The subsidence of the assumed ancient Pacific continent per- 
haps coincided with the great uplift during the late Cretaceous 
when most of the existing mountain systems of western America 
came into existence. 
AUSTRALASIAN-M ALAVSLAN GENERA OCCURRING IN HAWAII, BUT NOT IN AMERICA 
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