Interglacial Periods. Al 
of wood ?—a “ Noashina”’ and an ‘“‘Adamshina,”’ a kind which 
was drifted and another kind which grew on the spot. This 
is a point which will require to be determined. 
That so little has as yet been done in the way of searching 
for such evidence of interglacial periods, is, doubtless, in a 
great measure due to the fact that most of those, if not all, 
who have visited those regions entertained the belief that 
there is an @ priort improbability that a condition of climate 
which would have allowed the growth of trees in such a place 
prevailed so recently as Post-tertiary times. Hven supposing 
those Arctic voyagers had considered the finding of inter- 
glacial deposits a likely thing, and had in addition made 
special search for them, the simple fact that they should 
have failed to find any trace of them could not, as we have 
already shown, be regarded as even presumptive evidence 
that none existed. Take Scotland as an example. Abundant 
relics of interglacial age have there been found from time to 
time ; butamongst the many geologists who visit that country 
year by year, how few of them have the good fortune of dis- 
covering a single relic. In fact a geologist might search for 
months, and yet fail to meet with an interglacial deposit. The 
reason is obvious. The last ice-sheet, under which Scotland 
was buried, was so enormous as to remove every remnant of 
the preceding interglacial land-surface, except here and there 
in deep and sheltered hollows, or in spots where it may happen 
to have been protected from the grinding power of the ice 
by projecting rocks. But all those places are now so com- 
pletely covered with boulder-clay and other deposits that it 
is only in the sinking of pits, quarries, in railway-cuttings, 
and other deep excavations that traces of them accidentally 
turn up. Now if it is so difficult to find in temperate regions, 
in a place like Scotland, interglacial remains, how much more 
difficult must it be to meet with them in Arctic regions, where 
the destructive power of the ice must have been so much 
greater. 
Something like indications of an interglacial period appear 
to have been found by Professor Nordenskjéld in Spitzbergen. 
“Tn the interior of Ice-fjord,” he says, “and at several other 
_ places on the coast of Spitzbergen, one meets with indications 
either that the polar tracts were less completely covered with 
ice during the glacial era than is usually supposed, or that, 
in conformity with what has been observed in Switzerland, 
interglacial periods have also occurred in the polar regions. 
In some sandbeds not very much raised above the level of 
the sea one may, in fact, find the large shells of a mussel 
(Mytilus edulis) still living in the waters encircling the Scan- 
dinavian coast. It is now no longer found in the sea around 
