80 THE DEPTHS OF THE SEA. [CHAP. II. 
taining a remarkable system of oceanic circulation, 
and yet keeping so distinct from one another that 
an hour’s sail may be sufficient to pass from the 
extreme of heat to the extreme of cold. 
Finally, it had been shown that a large proportion 
of the forms living at great depths in the sea belong 
to species hitherto unknown, and that thus a new 
field of boundless extent and great interest is open 
to the naturalist. It had been further shown: that 
many of these deep-sea animals are specifically identi- 
cal with tertiary fossils hitherto believed to be extinct, 
while others associate themselves with and illustrate 
extinct groups of the fauna of more remote periods ; 
as, for example, the vitreous sponges illustrate and 
unriddle the ventriculites of the chalk. 
THORSHAVN, 
