HISTORY OF GEOLOGY. 



the Geography of Plants, and of Animals, and the History of theii 

 hange and diffusion ; intending by the latter subject, of course, 

 palcetiological History, the examination of the causes of what has 

 occurred, 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 Prin- 

 ciples of 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 briefly refer to some points, availing myself of his 

 labors and his ideas.' 



Sect. 2. Geography of Plants and Animals. 



WITH regard both to plants and animals, it appears, 1 that besides such 

 differences in the products of different regions as we may naturally 

 suppose to be occasioned by climate and other external causes ; an 

 examination of the whole organic population of the globe leads us to 

 consider the earth as divided into provinces, each province being occu- 

 pied by its own group of species, and these groups not being mixed or 

 interfused among each other to any great extent. And thus, as the 

 earth is occupied by various nations of men, each appearing at first 

 sight to be of a different stock, so each other tribe of living things is 

 scattered over the ground in a similar manner, and distributed into its 

 separate nations in distant countries. The places where species are 

 thus peculiarly found, are, in the case of plants, called their stations. 

 Yet each species in its own region loves and selects some peculiar con- 

 ditions of shade or exposure, soil or moisture : its place, defined by the 

 general description of such conditions, is called its habitation. 



Not only each species thus placed in its own province, has its posi- 

 tion further fixed by its own habits, but more general groups and assem- 

 blages are found to be determined in their situation by more general 

 conditions. Thus it is the character of the flora of a collection of islands, 

 scattered through a wide ocean in a tropical and humid climate, to 

 contain an immense preponderance of tree-ferns. In the same way, 

 the situation and depth at which certain genera of shells are found 

 have been tabulated* by Mr. Broderip. Such general inferences, if 



Lyell, Principles, B. iii. c. v. 2 Greenough, Add. 1835, p. 20 



