354 Wyville Thomson—General Ocean Circulation. 
thing of an abyssal character. These late researches tend to 
show that during past geological changes abyssal beds have 
never been exposed, and it seems highly probable that until 
comparatively recent geological periods such beds have not 
been formed. 
It appears now to be a very generally received opinion 
among geologists—an opinion which was first brought into 
prominence by Professor Dana—that the ‘“ massive” eruptions 
which originated the mountain chains which form the skeleton 
of our present continents, and the depressions occupied by our 
present seas date from the secular cooling and contraction of 
the crust of the earth—from a period much more remote than 
the deposition of the earliest of the fossiliferous rocks—and that 
during the period chronicled by the successive sedimentary 
systems, with many minor oscillations by which limited areas 
have been alternately elevated and depressed, the broad result 
has been the growth by successive steps of the original moun- 
tain chains and the extension of the continents by their denuda- 
tion, and the corresponding deepening of the original grooves. 
Tf this view be correct—and it certainly appears to me that the 
reasoning in its favor is very cogent—it is quite possible that 
until comparatively recent times no part of the ocean was suffi- 
ciently deep for the formation of a characteristic abyssal deposit. 
Time will not allow me even to allude to the interesting 
results which have been obtained from the determination o 
the density of sea water from different localities and different 
=a and from the analysis of sea water and its contained gases, 
an 
tory manner imaginable. 
year 1871 Count Wilezek, in the schooner Jsljérn, found the 
sea between Novaya Zemlya and Spitzbergen nearly free from 
ice, and that the same sea presented to Weyprecht and Payer 
in the following year a dangerous stretch of moving and im- 
ena pack. There can be no doubt that in the year 1861 
r. Hayes gazed over an expanse of open water where, in 
1875-76, Capt. Nares studied the conditions of paleocrystic ice. 
It is evident, therefore, that the Polar basin, or at all events 
