THE NORWEGIAN LEMMING AND ITS MIGRATIONS. 
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of our more familiar swallows, we find that the latter obviously 
seek a more genial climate and more abundant food, returning 
to us as surely as summer itself ; nor do they ever, so far as I 
know, breed on their passage. The swifts, which stay but a 
short time with us, remain in Norway barely long enough to 
rear their young before returning to Africa. It is difficult, in 
fact, to find a parallel case to that of the lemmings : the nearest 
approach, perhaps, is afforded by the strange immigration of 
Pallas’s sand-grouse in 1863, when a species whose home is on 
the Tartar Steppes journeyed on in considerable numbers to the 
most western shores of Europe, and very probably many perished, 
like the lemmings, in the waves of the Atlantic. But to revert 
to the swallows, which annually desert Europe to visit Africa. 
Let us suppose that these birds were partial migrants only — 
that is, that a remnant remained with us after the departure of 
the main body — and further suppose that the continent of Africa 
were to become submerged, would not many generations of 
swallows still follow their inherited migratory instincts, and 
seek the land of their ancestors through the new waste of waters, 
whilst the remaining stock, unimpeded by competition, would 
sooner or later, according to the seasons, recruit the ranks for a 
oew exodus ? It appears quite as probable that the impetus of 
migration towards this lost continent should be retained as that 
a dog should turn round before lying down on a rug, merely 
because his ancestors found it necessary thus to hollow out a 
couch in the long grass. 
W ell, then, is it probable that land could have existed where 
now the broad Atlantic rolls ? All tradition says so : old 
Egyptian records speak of Atlantis, as Strabo and others have 
told us. The Sahara itself is the sand of an ancient sea, and 
the shells which are found upon its surface prove that no longer 
ago than the Miocene period a sea rolled over what now is 
desert. The voyage of the 46 Challenger ” has proved the existence 
of three long ridges in the Atlantic Ocean, one extending for 
more than three thousand miles ; and lateral spurs may, by con- 
necting these ridges, account for the marvellous similarity in 
the fauna of all the Atlantic Islands. However, I do not 
suppose that the lemmings ever went so far south, though 
they are found as fossils in England ; but it is a remarkable 
fact that whilst the soundings off Norway are comparatively 
shallow for many miles, we find a narrow but deep channel 
near Iceland, which probably has prevented the lemming 
from becoming indigenous there, although an American species 
was found in Greenland during the late Arctic Expedition. If, 
as is probable, the Gulf Stream formerly followed this deep 
channel, its beneficent influence would only extend a few miles 
from the coast, which would also have reached to a great 
