GEOGRAPHICAL DISTRIBUTION OF ANIMALS 979 
The Galapagos Islands are a cluster of volcanic rocks 
lying in the open sea about six hundred miles to the west 
of Ecuador. On these islands is a peculiar land fauna, de- 
rived from South American stock, but mostly different in 
species. Darwin noted there “twenty-six land birds; of 
these, twenty-one, or perhaps twenty-three, are ranked as 
distinct species. Yet the close affinity of most of these 
birds to American species is manifest in every character, in 
their habits, gestures, and tones of voice.” 
Among land animals similar migrations may occur, giv- 
ing rise, through the adaptation to new conditions, to new 
species. The separation of species of animals isolated in 
river basins or lakes often permits the acquisition of new 
characters, which is the formation of distinct species in 
similar fashion. On the west side of Mount Whitney, the 
highest mountain in the Sierra Nevada of California, there 
is a little stream called Volcano Creek. In this brook is a 
distinct species or form of trout, locally called golden 
trout. It is unusually small, very brilliantly colored, its 
fins being bright golden, and its tiny scales scarcely over- 
lap each other along its sides. This stream flows over a 
high waterfall (Agua Bonita) into the Kern. River. The 
Kern River is full of trout, of a kind (Salmo gilberti) to 
which the golden trout is most closely allied. There can 
not be much doubt that the latter is descended from the 
former. With this assumption, it is easy to suppose that 
once the waterfall did not exist, or that through some 
agency we can not now identify certain fishes had been 
carried over it. Once above it, they can not now return, 
nor can they mix with the common stock of the river. 
Those best adapted to the little stream have survived. 
The process of adaptation has gone on till at last a distinct 
species (or sub-species*) is formed. In recent times the 
* In descriptive works the name species is applied to a form when 
the process of adaptation seems complete, When it is incomplete, or 
