DISTRIBUTION OF ORGANISMS. 207 



chronology. Startling as it may appear, we are now assured 

 that the present great continent comprising Europe, Asia, 

 and Africa, has been, with minor changes in the relative 

 position of sea and land, one theatre of organic being since 

 the commencement of the existence of land animals upon the 

 surface of the earth ; that is to say, there has been, on one 

 part or another of this geographical area, an uninterrupted 

 chain of living forms from an early period in the secondary 

 formation. This is the zoological province whose history is 

 presented by the geologists ; it is the oldest we are acquainted 

 with. There are, however, some isolated regions which are 

 known with certainty to have been in a condition of dry 

 land for a less space of time. Such are the volcanic islands, 

 of which the Isle of Bourbon is an example. Such also are 

 the Galapagos islands, placed in the Pacific, above five hun- 

 dred miles from South America. Now it is remarkable 

 in such regions to find the mammalia either wholly wanting 

 or in very small numbers. 



Australia itself a fifth great section of the habitable 

 globe appears to be one of these regions of an incomplete 

 zoology. It is well known to have no native mammalia 

 besides that humble implacental kind which are nearly 

 peculiar to it, and a few rodents and bats. Professor Owen 

 remarks how the fishes of the oolitic era acrodus psammodus, 

 etc. with the contemporary mollusks (trigoniae and terebra- 

 tulae), which served these fishes for food, are represented in 

 the living cestraceon which swims the Australian seas, with 

 exactly the same sea mollusks to yield them sustenance. 

 "Araucariae and cycadeous plants likewise," he says, " flourish 

 on the Australian continent, where marsupial quadrupeds 

 abound, and thus appear to complete a picture of an ancient 

 condition of the earth's surface, which has been superseded 

 in our hemisphere by other strata and a higher type of mam- 

 malian organization/Y 83 ) 



Such being the facts of the case, we are to inquire whether 

 they best agree with the hypothesis of an origin of organisms 

 by special Divine exertion, or that of their origination in 

 Divine power working in the manner of natural law ; and 



