CH. V] LIMITS OF AUSTRALIAN REGION. 223 



coincides with a line marking off the range of the Indo- 

 Malayan and Pacific races of mankind. This remarkable 

 series of facts is usually accounted for in the following 

 way. The greater depth of water between the islands 

 mentioned probably indicates a longer time or separation 

 from each other than in those cases where the dividing 

 seas are shallower. Hence it may be assumed that the 

 dominant race of Mammalia in the earlier periods of the 

 earth's history occupied Australia in common with the 

 rest of the world ; at this time the deep separation 

 between the two regions, as we now admit them, took 

 place. Australia and the Australian region generally 

 would be well stored with Marsupials. So too would the 

 Oriental region. But in course of time the wave of 

 migration of higher types of mammals, the placental 

 mammals, evolved gradually from the Marsupial, would 

 extend eastward and improve the remaining Marsupials 

 off the face of the world ; the deep straits already referred 

 to might be reasonably held to offer an impediment to 

 their further progress eastward in sufficient numbers at 

 any rate to compete successfully with the mammalian 

 possessors of the soil. As a matter of fact the fringes of 

 the Australian region, the islands of Lombok and Celebes, 

 to wit, have received some few of these later migrants ; 

 " a baboon, a wild cat and a squirrel " occur in Celebes ; 

 while Macacus cynomolgus and one or two other placental 

 mammals reside in Lombok. This appears to be a 

 feasible explanation of the facts. But as already hinted 

 there are difficulties in the way of its immediate accept- 

 ance. To begin with, remains of the elephant have been 



