412 THE POPULAR SCIENCE MONTHLY. 



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 westei-n shores of Europe, and very probably many per- 

 ished, 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 sub- 

 merged, 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, while the remaining stock, unim- 

 peded by competition, would sooner or later, according to the seasons, 

 recruit the ranks for a new exodus ? It appears quite as probable 

 that the impetus of migration toward this lost continent should be re- 

 tained 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 gi-ass. 



Well, 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 

 npon its surface prove that no longer ago than the Miocene period a 

 sea rolled over what now is desert. The voyage of the Challenger 

 has proved the existence of three long ridges in the Atlantic Ocean, 

 one extending for more than 3,000 miles ; and lateral spurs may, by 

 connecting these ridges, account for the marvelous 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, while the sound- 

 ings off Norway are comparatively shallow for many miles, we find a 

 narrow but deep channel near Iceland, which probably lias 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 distance beyond the present 

 shores of Norway, and thus the lemmings would have acquired the 

 habit of traveling westward in search of better climate and more 

 abundant food ; and, as little by little the ocean encroached on the 

 land, the same advantages would still be attained. And thus, too, 

 we find an explanation of the fate which befalls the adventurous wan- 

 derers ; for we have already seen that no lake deters them, and that 

 they frequently cross the fjords, or arms of the sea, in safety. No 



