402 
thirdly by isostatic uplift of the land, which latter considerably 
retards the effect of denudation. For the present I will leave those 
phenomena out of consideration, because they cannot materially 
have affected the oscillations of the sea-level dealt with in this paper. 
The validity of the above theory can hardly be called in question, 
anyhow not if we assume that in the glacial period ice-masses of 
considerable thickness, on an average 1000—1200 m., were accu- 
mulated over a vast extent on the land in polar regions. Thus far, 
however, its validity has not been tested for considerable areas of the 
earth’s surface by the relations observable at present along the coasts. 
In tropical regions these tests will be simpler and must yield 
more precise results than outside the tropics. For outside the trop- 
ies, especially in the regions bordering immediately on the regions 
glaciated in the ice-age, the phenomenon of shifts of the sealevel, 
depending on the greater or smaller extent of the polar ice-caps, is 
rendered indistinct through the interference of the above-named influ- 
ences, which are very operative outside the tropics, and on the 
contrary are hardly perceptible in the tropical regions ‘). 
Furthermore, such a test can be effectual only in regions not 
affected by tectonic movements since the close of the Pliocene. 
There is, therefore, a reasonable chance of the possibility to trace and 
to discriminate the displacements of the shorelines, caused by the 
') This does not mean to say that the oscillations of the sealevel in consequence 
of the pleistocene ice-age are not distinguishable in temperate zones. [t will be 
more difficult to identify the phenomenon there, since it has first to be severed 
from the additional influences mentioned above, whose magnitude relative to that 
of the main phenomenon, is nol sufficiently known. On the other hand, there is 
a factor that could be utilized in the neighbourhood of the glaciated regions, viz. 
the fact that there the consecutive glacial and interglacial periods will manifest 
themselves through variations in the marine fauna. At the commencement of the 
glacial period the first approach of the ice in the northern hemisphere will 
have revealed itself by the introduction of arctic types into the marine fauna. We 
know that this is noticeable in the latter part of the pliocene period in England 
and in Holland, and that, therefore, the assertion that the ice-age commenced 
already in what is generally called “Upper Pliocene’, is not unfounded. In tropical 
regions, on the contrary, the allernate interglacial and glacial times wiil presumably 
not have exerted an appreciable influence upon the fauna, so that in this respect 
the researches in tropical climes will have to do without a factor that is available 
outside the tropics. Taking everything into consideration the shift of the coast-line 
consequent on the alternate growth and melting of the polar ice-caps, will prove 
to be so much more regular and less modified through other influences in the 
tropical regions than elsewhere that a critical examination in the tropical regions 
is far preferable to one in the temperate zones, at all events a far as the main 
features of the phenomenon are concerned. 
