230 THE DOCTRINE OF DESCENT. 
volcanic and coral islands only such animals will be 
encountered as reached them by swimming or flying. 
The presence of Mammals pre-supposes human agency 
or extraordinary accidents. The older the islands, the 
richer are they in organisms. Islands detached from 
continents will, on the contrary, be rich in proportion 
as they are recent, of which Great Britain bears witness. 
The more divergent is their fauna, the longer must be 
the time which has elapsed since their separation. Thus, 
for instance, we may view the relations of Tasmania 
and Australia; and if New Zealand was ever connected 
with the old Australian continent, the separation occur- 
red at an epoch so remote that it throws no light upon 
the physiognomy of the animal world-of New Zealand, 
and vice versa. 
In the account of his travels in the Malay Archipelago, 
Wallace has given a pattern of animal-geographical 
research, Years before, G. Windsor Earl had pointed 
out that the great islands of Sumatra, Borneo, and Java, 
are connected with the Asiatic continent by a shallower 
sea; while a similar shallow sea assigns New Guinea 
and several adjacent islands to Australia, with which 
they have a common characteristic in the Marsupials. 
Wallace has defined this partition more minutely with 
a line marked by a deeper submergence of the sea- 
bottom. It is drawn below the Philippine Islands, 
and, having Celebes to the south, passes through the 
straits of Macassar and separates the two small islands 
of Bali and Lombok. We will now follow Wallace’s 
description (“Malay Archipelago”), with various omis- 
sions. : 
“It is now generally admitted that the present dis- 
