No. 410.] THE EUROPEAN FAUNA. IO9 
and Ireland except over the land connection with France. 
But how did they get into France? Where did they originally 
come from? Various reasons preclude any hypothesis of these 
animals being part of the Oriental invasions, ànd the offshoot of 
the later, the Alpine fauna. Their relationships are decidedly 
Siberian, not central or south Asiatic, and the lemmings, as 
well as the willow ptarmigan, are quite foreign to the Alps. 
I have already expressed my agreement with Dr. Scharff that 
they do not form part of the great later Siberian invasion ; they 
were present in northern Europe long before that event, as 
shown by their history in the British Islands. 
It goes without saying that the relationships of these Arctic 
animals are decidedly northern and, as already remarked, 
equally closely Siberian, and I have no doubt that northern 
and western Siberia was their home, before they invaded 
western Europe. I am therefore compelled to recognize two 
distinct Siberian invasions (or rather three, since a third one 
is in progress to-day) widely separated in time. 
The first Siberian invasion (Scharff's Arctic) took place 
early, probably before the first great glaciation had reached its 
maximum. Neither ice nor water had yet shut off the passage 
north of the Caspian Sea and along the northern edge of the 
central European mountain ranges. Thus the Tundra reindeer, 
the variable hare, the ermine, the Norwegian lemming, the 
ptarmigan, the willow grouse, and others penetrated westward 
to France (and the Pyrenean peninsula) and over the then con- 
tinuous England, Ireland, and Scotland to western Norway 
without leaving any traces in the continental boulder clay 
which was deposited only after they had passed. The maxi- 
mum of the first glaciation then barred the further ingress of 
any more Siberians; the boulder clay was deposited next, and 
on the retreat of the glaciers or rise of the land, — or rather 
both, — the second Siberian invasion, among which were several 
of the same species as the first, took place over the boulder clay. 
It is my impression that the musk ox and the banded lemming 
(Cuniculus torquatus) formed part of the first invasion, but for 
some reason or other failed to reach sufficiently far west and 
north early enough to pass into Ireland or Norway. It may 
