Malaysian Phytogeography and Polynesian Flora 253 



islands. In general, this same statement applies to the plants. 

 Mere proximity to Asia or Australia is, in part, the cause of this 

 condition, but a brief consideration of geologic history will pro- 

 vide a fuller explanation. 



The Tertiary was the period of the development and dissem- 

 ination of mammals. The mammals were very poorly repre- 

 sented in Australia, where their place was taken by the more 

 primitive marsupials. It seems evident that, in earlier geologic 

 times, Australia was definitely united with Asia, but was sepa- 

 rated from it before the mammals became dominant. This in 

 part explains the plant and animal forms, long-continued isola- 

 tion favoring local development uninfluenced by direct migrants 

 from Asia. In pre-Tertiary times, intermigration was possible 

 until the late Cretaceous; since that time most northwestern- 

 southeastern intermigrations have been inhibited by the con- 

 stant archipelagic conditions of certain parts of Malaysia, and 

 since the late Cretaceous or early Tertiary there apparendy have 

 been no direct land-connections between Asia and Australia. In 

 the Tertiary, there were great physical changes in a large part of 

 Malaysia, as is evidenced by the greatly developed Tertiary sedi- 

 ments in the Archipelago, but always, somewhere, there were 

 apparently large land areas in existence. 



MolengraaflF has clearly indicated the probable geologic history 

 of this region since the Tertiary.* There have been two fairly 

 stable continental areas and an intermediate unstable insular 

 area. The Asiatic bank, or Sunda shelf, extending southward 

 from Asia, comprising approximately 1,850,000 square kilo- 

 meters, carries upon it the Malay Peninsula, Sumatra, Java, and 

 the smaller islands eastward to Bali, Borneo, and the Palawan- 



* Molengraaff, G. A. F., 1921. Modern deep-sea research in the East Indian 

 Archipelago. Geogr. Jour., 57:95-121. f.1-9. map. 



