IS92.] 
461 
[De Geer. 
submergence are also found at the southern shore of the Baltic 
and around the North Sea. 
It is not yet possible to say anything with certainty about the 
nature of this last oscillation ; but while there seem to be some dif- 
ficulties in such an explanation, it may be possible that we have to 
deal here only with oscillations in the situation of the pivot point 
of the crust-movement or the isobase for zero. Professor N. S. 
Shaler has suggested , 1 that while the continents are as a rule ris- 
ing and the sea-floors sinking, yet it may happen that the 
pivot point, when it lies somewhat at the inside of the shore, will 
take part in the sinking of the sea-bottom, and then it will seem 
as if the continent were sinking, though in fact it may very well 
be rising in the interior. If it should turn out that this ingenious 
explanation could be applied to the Scandinavian oscillations of 
land, then the whole phenomenon would be more easily under- 
stood ; according to this theory, in the center of the region after 
the removal of the ice-load a constant rising of the land oc- 
curred, and at the same time probably a sinking of the sur- 
rounding sea-bottom, in which latter movement some portions 
of the land for a time took part during the post-glacial subsidence. 
After that, the portions mentioned began again to participate in 
the great continental upheaval, which seems to be still going on 
though probably at a much reduced rate. 
Investigations in North America. 
Observations. 
The very interesting and valuable investigations of Gilbert, Up- 
ham, and Spencer have shown that the shore-lines along the 
great lakes in the interior of eastern North America have been 
unequally uplifted more toward the north than toward the south, 
and this seems to be quite in accordance with the generally 
adopted opinion in regard to the marine deposits along the Atlan- 
tic coast. This opinion seems to have been founded principally 
upon the different heights to which marine shells could be traced 
in different tracts, this kind of evidence being the most indis- 
putable, though on the other hand affording only minimum fig- 
ures. Concerning other proofs, as shore-lines, terraces, deltas, 
1 Recent changes of level on the coast of Maine. Mem. Bost. soc. nat. hist., v. 2, 
p. 337, 1874. 
