5 2 9 
even some vegetation on their surfaces, and extensive 
level ice-fields break away and float southwards. Again, 
uprooted trees and rafts of driftwood are often floated 
down great rivers and carried out to sea. Such rafts or 
islands are sometimes seen floating a hundred miles— 
monkeys, tiger-cats, and squirrels have been seen upon 
some of them. Even small and weak birds are often 
carried accidentally across great widths of ocean by violent 
gales. Migrants flying along the eastern coast of the 
United States are blown out to sea to the Bermudas. 
Hurricanes and whirlwinds often gather up considerable 
quantities of water, and with it fishes of small size. Eggs 
of fish are carried by aquatic birds ; aquatic birds feed on 
these eggs and sometimes they are not destroyed, but pass 
through the body unimpaired. 
Now, with regard to these “means of dispersal,” the 
first thing that strikes us is the precarious nature of the 
process of migration. Mammals may be carried out to 
sea, but it does not at all necessarily follow that their raft 
will ever reach land, and if they get washed off their raft, 
or the raft itself breaks up, they will become food for 
fishes. Masses may break off from the end of the glacier 
which hangs over the sea, and the iceberg thus formed 
may carry seeds and plants and perhaps some animals 
upon it, but this fact will not avail unless the floating 
iceberg come in contact with solid land. The bird which 
has just filled its crop, and the bird of prey which has 
made a meal off a bird which has just filled its crop, with 
seeds, may convey these seeds to a considerable distance ; 
but it will avail nothing if the birds are not killed after a 
short time, and on land where these seeds will grow. 
When we consider the risks which must necessarily accom 
pany such voyages, it is allowable to believe that only a 
few favoured individuals will reach a new habitat. 
HH