I THE INTRODUCTION OF NEW SPECIES 11 
readily account for the exceptions and apparent discrepancies 
that here and there occur. The writer’s object in putting 
forward his views in the present imperfect manner is to 
submit them to the test of other minds, and to be made 
aware of all the facts supposed to be inconsistent with them. 
As his hypothesis is one which claims acceptance solely as 
explaining and connecting facts which exist in nature, he 
expects facts alone to be brought to disprove it, not & priori 
arguments against its probability. 
Geological Distribution of the Forms of Life 
The phenomena of geological distribution are exactly 
analogous to those of geography. Closely allied species are 
found associated in the same beds, and the change from 
species to species appears to have been as gradual in time as 
in space. Geology, however, furnishes us with positive proof 
of the extinction and production of species, though it does 
not inform us how either has taken place. The extinction of 
species, however, offers but little difficulty, and the modus 
operandi has been well illustrated by Sir C. Lyell in his ad- 
mirable Principles. Geological changes, however gradual, 
must occasionally have modified external conditions to such 
an extent as to have rendered the existence of certain species 
impossible. The extinction would in most cases be effected 
by a gradual dying-out, but in some instances there might 
have been a sudden destruction of a species of limited range. 
To discover how the extinct species have from time to time 
been replaced by new ones down to the very latest geological 
period, is the most difficult, and at the same time the most 
interesting problem in the natural history of the earth. The 
present inquiry, which seeks to eliminate from known facts 
a law which has determined, to a certain degree, what species 
could and did appear at a given epoch, may, it is hoped, be 
considered as one step in the right direction towards a com- 
plete solution of it. 
High Organisation of very ancient Animals consistent 
with this Law 
Much discussion has of late years taken place on the 
question whether the succession of life upon the globe has 
