Nansen's Continental Oscillations — Spencer. 235 
time when he made the studies just referred to by Nansen, 
he was the pioneer in searching into these deep drowned 
valleys, without the suggestive assistance of Prof. Hull and 
Dr. Nansen, and the whole problem was too great for one 
worker. So when he comes to revise his earlier studies, 
they will have the great advantage of the new light now 
thrown on the question, and doubtless there will be close 
agreement in our views, when dealing with the same 
phenomena, for in such discordance as referred to he 
thinks "that there may be other explanations, and he does 
not consider it necessary to assume that the continental 
shelf has undergone the same changes of level along its- 
whole length — even though at some places it may have 
been elevated more than 1,000 metres and again low- 
ered to its original position" (p. 199). The "facts indicate 
that on one hand there has been during very long periods 
a certain stability of sea level," but at the same time "great 
oscillations above and below sea level * * * have oc- 
curred at different periods." Also "a late and more uni- 
versal rise of sea level of perhaps 100 metres or more ac- 
companied by perhaps several oscillations of the same 
kind." A' crust floating on the underlying magma he 
compares with an unequally loaded ice-floe subjected to- 
changing "ice-pressures." The thermal contraction and 
expansion of the rocks, are discussed at some length as to 
their bearing on the changes of level, and it is perhaps the 
most suggestive consideration, although the transposition 
of the land-waste to the sea, accumulation of glaciers and 
their melting, etc., are considered. There seems no satis- 
factory explanation of the cause of the great changes of 
level of the land and sea, but after each disturbance there 
is a tendency to return to equilibrium, "probably determined 
by the buoyancy of the crust floating on a liquid magma" 
(p. 213). "A theory which would explain the above facts 
must recognize the tendency, whether the disturbances 
be due to the lithosphere or hydrosphere" (p. 200). 
