Deposits i)i the Magellan Territories. — Nordoiskjold. 309 
as regular in their reappearance. For if we know that glacial 
periods have occurred in so many parts of the world's surface, 
far distant from each other within one and the same, from a 
geological standpoint, short epoch, all the three hypotheses 
mentioned, that concern themselves with forces that must 
always have acted throughout the whole of the geological 
periods, to be probable premise that a number of cold periods 
must have existed even during the preceding and considerably 
more prolonged period of the Tertiary epoch. Since now no 
manifest traces of that have been come upon in any region 
the most plausible view is one that endeavors to explain the 
glacial period as being, due to some temporary cosmic phe- 
nomenon that exercised its influence uniformly over the whole 
earth. That phenomenon had not strength enough to sub- 
induce a covering of ice throughout the polar lands; for East 
Siberia had none. On the other hand it is open to doubt 
whether it occurred suddenly and lasted but a short time com- 
paratively, and whether it thus caused a simultaneous glacia- 
tion in all districts where it was by reason of the conditions 
of temperature and humidity possible to do so, or whether, as 
is more likely, its effects were only gradual but prolonged, 
possibly through the whole of the Pliocene and Pleistocene 
periods, but that it was too ineffectual to cause a genuine 
glacial period, save in places where favourable local circum- 
stances were at hand to promote it. In this connection it is 
not impossible that the facts, upon which the Croll hypothesis 
builds, may have a considerable importance. 
What that cosmic phenomenon can have been we at pres- 
ent do not know. I cannot, however, refrain from mention- 
ing, as one of the most plausible views hitherto put forth, that 
of Arrheniu?*and Hogbom, viz: that the cold climate during 
the glacial period was caused by a lowering of the percentage 
of carbon anhydride in the air. while the warm climate during 
the earlier part of the Tertiary period was due to a corre- 
sponding increase of the same.f 
*S. Arrhenius. Phil. Mag.. S. 5. vol. XLI (1896) i.. 22,T. Cf. also 
T. C. Chainberlin, Journal of Geology, V, 653. 
t A more complete discussion of the geology of the Magellan terri- 
tories is to appear in "Wissenschaftliche, Bcobachtungen wiihrend 
fier Schvved. Expedition nach den Magellanlandem," now in the press. 
