138 TERTIARY ROCKS OF AUSTRALASIA, 



derful physical changes that have taken place in this 

 region within the periods. In Wallace's Island Life, 

 pp. 460-467, a most graphic account is given of these 

 changes with respect to their influence upon the spread of 

 organic life. The conclusions arrived at by Mr. Wallace 

 and ProfessoV Hutton, based upon these terrestrial changes, 

 throw much light upon the problems connected with the 

 origin and spread of existing forms of life throughout 

 Australasia, and the writer cannot do better than reproduce 

 an abstract of Mr. Wallace's views in his own words ; 

 thus, p. 462 : " If we imagine the greater part of North 

 Australia to have been submerged beneath the ocean, from 

 which it rose in the middle or latter part of the Tertiary 

 period, offering an extensive area ready to be covered by 

 such suitable forms of vegetation as could first reach it, 

 something hke the present condition of things would 

 inevitably arise . . . The existence in North and 

 North-east Australia of enormous areas covered with 

 Cretaceous and other Secondary deposits, as well as exten- 

 sive Tertiary formations, lends support to the view that 

 during very long epochs temperate Australia was cut off 

 from close connection with the tropical and northern lands 

 by a wide extent of sea ; and this isolation is exactly 

 what was required in order to bring about the wonderful 

 amount of specialisation and the high development mani- 

 fested by the typical Australian flora . . ." From a 

 study of the South-eastern and South-western Austrahan 

 flora he also infers that the "facts clearly point to the 

 conclusion that South-western Australia is the remnant of 

 the more extensive and more isolated portion of the con- 

 tinent in which the peculiar Australian flora was prin- 

 cipally developed. The existence there of a very large 

 area of granite — 800 miles in length by nearly 500 in 

 maximum width — indicate such extension ; for this granitic 

 mass was certainly buried under piles of stratified rock, 

 since denuded, and then formed the nucleus of the old 

 Western Australian continent. But while this rich and 

 peculiar flora was in process of formation, the eastern 

 portion (the Cordillera) of the continent must either have 

 been widely separated from the western, or had, perhaps, 

 not yet risen from the ocean. If we examine the geo- 

 logical map of Australia ... we shall see good reason 

 to conclude that the eastern and western divisions of the 



