Ch. IV.] 



PROVED BY ORGANIC REMAINS. 43 



shown to have been contemporaneous, if we suppose the rivers 

 flowing from those three countries to carry the remains of 

 different species of the animal and vegetable kingdoms into the 

 Mediterranean. 



In like manner, the sea intervening between the northern 

 shores of Australia and the islands of the Indian ocean, con- 

 tains a great proportion of the same species of corallines and 

 testacea, yet the land animals and plants of the two regions are 

 very dissimilar, even the islands nearest to Australia, as Java, 

 New Guinea, and others, being inhabited by a distinct assem- 

 blage of terrestrial species. It is well known that there are 

 calcareous rocks, volcanic tuff, and other strata in progress, in 

 different parts of these intermediate seas, wherein marine 

 organic remains might be preserved and associated with the 

 terrestrial fossils above alluded to. 



As it frequently happens that the barriers between differ- 

 ent provinces of animals and plants are not very strongly 

 marked, especially where they are determined by differences of 

 temperature, there will usually be a passage from one set of 

 species to another, as in a sea extending from the temperate to 

 the tropical zone. In such cases, we may be enabled to prove, 

 by the fossils of intermediate deposits, the connexion between 

 the distinct provinces, since these intervening spaces will be 

 inhabited by many species, common both to the temperate and 

 equatorial seas. 



On the other hand, we may be sometimes able, by aid of a 

 peculiar homogeneous deposit, to prove the former coexistence 

 of distinct animals and plants in distant regions. Suppose, for 

 example, that in the course of ages the sediment of a river, like 

 that of the Red River in Louisiana, is dispersed over an area 

 several hundred leagues in length, so as to pass from the tropics 

 into the temperate zone, the fossil remains imbedded in red 

 mud might indicate the different forms which inhabited, at the 

 same period, those remote regions of the earth. 



It appears, then, that mineral and organic characters, although 

 often inconstant, may, nevertheless, enable us to establish the 



