620 HISTORY OF GEOLOGY. 



ordinary general facts have naturally put in activity 

 very bold speculations. 



But, as has already been said, we cannot spe- 

 culate upon such facts in the past history of the 

 globe, without taking *a large survey of its present 

 condition. Does the present animal and vegetable 

 population differ from the past, in the same way in 

 which the products of one region of the existing 

 earth differ from those of another ? Can the crea- 

 tion and diffusion of the fossil species be explained 

 in the same manner as the creation and diffusion of 

 the creatures among which we live? And these 

 questions lead us onwards another step, to ask, 

 What are the laws by which the plants and animals 

 of different parts of the earth differ? What was the 

 manner in which they were originally diffused? 

 Thus we have to include, as portions of our subject, 

 the Geography of Plants, and of Animals, and the 

 History of their change and diffusion; intending by 

 the latter subject, of course, palaztiological History, 

 the examination of the causes of what has occur- 

 red, and the inference of past events, from what we 

 know of causes. 



It is unnecessary for me to give at any length 

 a statement of the problems which are included in 

 these branches of science, or of the progress which 

 has been made in them ; since Mr. Lyell, in his work 

 on Geology, has treated these subjects in a very 

 able manner, and in the same point of view in 

 which I am thus led to consider them. I will only 



