158 MAMMALS OF THE PACIFIC WORLD 



rated by relatively shallow seas or straits from the mainland 

 and connected with it at various times in the history of the 

 earth. Oceanic islands have never been connected with a con- 

 tinent but are separated from it by water of great depth — 

 more than six hundred feet. They have arisen from the floor 

 of the ocean. In a few cases it is uncertain whether certain is- 

 lands are continental or oceanic, whether the former connec- 

 tions with the mainland have foundered or whether the island 

 has been pushed up from the bottom of the sea. 



Examples of continental islands are the Greater Sundas — 

 Sumatra, Java and Borneo — Japan and Formosa, formerly 

 connected with confinental Asia. Similarly, New Guinea was 

 once joined to Australia. The shallow seas now separating such 

 islands from their mainlands were probably dry land during the 

 last ice age. Many mammals which occurred in neighboring 

 areas of the continents were able to spread to the islands with- 

 out difficulty. At the end of the ice age the gradually rising seas 

 again isolated the islands with the animals which had invaded 

 them. The mammals inhabiting continental islands differ only 

 slightly or not at all from those of the nearby continents ; an- 

 cient types of animals, known as "living fossils," are usually 

 absent. 



The Luchu and Kurile Islands seem to represent parts of 

 former continental areas that sank. The higher peaks of for- 

 mer coastal ranges were left as islands, cut off from each other 

 and Japan, Formosa, and Kamchatka by deep straits. Move- 

 ments of the earth's crust have also thrown up great interior 

 mountain ranges on land; in some cases these ridges continue 

 out onto the floor of the ocean. Such plunging mountain ranges 

 as the Aleutians occur, the landward members of which are con- 

 tinental, but the distant peaks have always been separated by 

 deep straits from the mainland. 



Celebes, the Moluccas, the Philippines, and Australia may 

 have been parts of an ancient southeastern extension of the 

 Asiatic continent. If this be true, this area must have been 



