HUMBOLDT, DARWIN, AND WALLACE. 351 
phenomena of which may ‘be explained with remarkable 
simplicity and clearness by the theory of selection. I 
mean Chorology, or the theory of the local distribution of 
organisms over the surface of the earth. By this I do 
not only mean the geographical distribution of animal 
and vegetable species over the different parts and provinces 
of the earth, over continents and islands, seas, and rivers ; 
but also their topographical distribution in a vertical 
direction, their ascending to the heights of mountains, and 
their descending into the depths of the ocean. (Gen. 
Morph. ii. 286.) 
The strange chorological series of phenomena which 
show the horizontal distribution of organisms over parts of 
the earth, and their vertical distribution in heights and 
depths, have long since excited general interest. In recent 
times Alexander Humboldt *? and Frederick Schouw have 
especially discussed the geography of plants, and Berghaus 
and Schmarda the geography of animals, on a large scale. 
But although these and several other naturalists have in 
many ways increased our knowledge of the distribution of 
animal and vegetable forms, and laid open to us a new 
domain of science, full of wonderful and interesting 
phenomena, yet Chorology as a whole remained, as 
far as their labours were concerned, only a desultory 
knowledge of a mass of individual facts. It could not be 
called a science as long as the causes for the explanation of 
these facts were wanting. These causes were first disclosed 
by the theory of selection and its doctrine of the migrations 
of animal and vegetable species, and it is only since the 
works of Darwin and Wallace that we have been able to 
speak of an independent science of Chorology. 
