Ix THE DEBT OF SCIENCE TO DARWIN 469 
of special creations, had no scientific existence. It is to 
Darwin that we owe the establishment of the distinction of 
oceanic from continental islands, while he first showed us the 
various modes by which the former class of islands have been 
stocked with life. By a laborious research in all the accounts 
of old voyages, he ascertained that none of the islands of the 
great oceans very remote from land possessed either land 
mammalia or amphibia when first visited; and on examina- 
tion it is found that all these islands are either of volcanic 
origin or consist of coral reefs, and are therefore presumably 
of comparatively recent independent origin, not portions of 
submerged continents, as they were formerly supposed to be. 
Yet these same islands are fairly stocked with plants, insects, 
land-shells, birds, and often with reptiles, more particularly 
lizards, usually of peculiar species, and it thus becomes 
important to ascertain how these organisms originally reached 
the islands, and the comparative powers different groups of 
plants and animals possess of traversing a wide extent of ocean. 
With this view he made numerous observations and some 
ingenious experiments. He endeavoured to ascertain how 
long different kinds of seeds will resist the action of salt 
water without losing their vitality, and the result showed 
that a large number of seeds will float a month without 
injury, while some few survived an immersion of one hundred 
and thirty-seven days. Now, as ocean currents flow on the 
average thirty-three miles a day, seeds might easily be carried 
1000 miles, and in very exceptional cases even 3000 miles, 
and still grow. Again, it is known that drift-timber is often 
carried enormous distances, and some of the inhabitants of 
the remote coral-islands of the Pacific obtain wood by this 
means, as well as stones fastened among the roots. Now, 
Darwin examined torn-up trees, and found that stones are 
often inclosed by the roots growing round them so as to leave 
closed cavities containing earth behind; and from a small 
portion of earth thus completely inclosed, he raised three 
dicotyledonous plants. Again, the seeds that have passed 
through the bodies of birds germinate freely, and thus birds 
may carry plants from island to island. Earth often adheres 
to the feet of aquatic and wading birds, and these migrate to 
enormous distances and visit the remotest islands, and from 
