24 Geological Effects of a Varying Rotation of the Earth, | January, 
come of the former tops of other islands, which certainly must d 
have been in existence, to form the bases of many of the presents t 
atolls, and for a connecting stage between the successive depres- 
sions according to our theory? it may be replied, that they ` 
may have been carried away by the waves in the period of up- 
heaval. We may, perhaps, see some evidence of this, where some 
atolls are themselves arranged in a ring-like form, as though an 
older atoll had been shattered, and each remnant became the cen- 
ter ofa smaller one, as is the case in Atoll Ari, and in the Mal- : 
dives generally. 
Falling into the same line of argument is Darwin's observation 
of the terraces, on the Island of San Lorenzo, opposite Callao. 
EAE e Pain 
He found there evidence of three terraces, and on the lowest, at — 
an altitude of eighty-five feet, recent shells, but they were deeply 
corroded, and had “a much older and more decayed appear- 
ance, thon those at a height of 500-600 feet on the coast one 
Chili.’ 
Professor Dana, in his work on coral islands, argues strongly — 
Te 
aaa ipa 
in favor of recent tropical depressions, in not only the Pacific and ‘ 
Indian oceans, but in the Atlantic also, even including many areas 
which Darwin considers to have been elevated. He also con- — 
siders them as being compensated by elevations in higher lati- _ 
tudes preceding or during the Glacial period. 
As before suggested, it does not seem to the writer necessary 
to assume a continuous subsidence from that time, perhaps inter- 
rupted with periods of stability, but rather that there may have ~ 
been at least one time of considerable elevation intervening. Our 
hypothesis may assist in explaining certain problematic questions 
of this age, viz.: The occurrence of European plants in Australia, 
by the elevation of the tropical regions, at the proper time to form — 
a bridge between the Palearctic and Australian provinces, and 
the occurrence of numerous edentates in North America towards 
the end of the Glacial period, by the elevation of the regions be- 
tween North and South America. 
3. Changes in Earlier Ages, 
It is quite generally recognized by geologists, that in earlier — 
times the land and sea were subject to oscillations of continental — 
extent. Indeed, Europe and North America seem to have risen © 
and subsided contemporaneously. Considering that conglomer- 
ates indicate recent elevation of the land, and perhaps a culmina- — 
