THE INTRODUCTION OF NEW SPECIES 



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 h 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 been replaced by new ones down to the very latest geological 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 



