46 COMPENDIUM OF GEOGRAPHY AND TEAVEL 



account for the absence of so many important groups of 

 mammalia. Two explanations are open to us. Either 

 the former union with Borneo, and, perhaps, with For- 

 mosa, w^as limited in extent and of short duration, so 

 that only a few mammalian types ever entered the 

 country ; or, the union having been more complete and 

 of sufficient duration, the islands became well stocked 

 with mammals, but a great amount of subsidence has 

 since so reduced the land area and altered the physical 

 conditions, that numbers of them, especially those of the 

 largest size, have become extinct. This latter hypothesis 

 is supported by the fact, that almost everywhere are found 

 large tracts of elevated coral reefs containing shells simi- 

 lar to those now living in the adjacent seas — proving that 

 at a comparatively recent period the islands have been 

 partially submerged, and therefore less extensive than 

 they are now. Mr. Eolfe, too, considers the present flora 

 to have been differentiated when the islands were much 

 more immersed than is now the case. We know that 

 all volcanic countries are subject to elevations and sub- 

 sidences, and it is highly probable that so pre-eminently 

 volcanic a district as the Philippines has been repeatedly 

 subject to partial elevations and depressions ; at one time 

 eliecting a union with adjacent lands, and thus favouring 

 the introduction of new animals, at another submerging 

 extensive areas, and thus leading to the extermination of 

 many forms of life. Changes of this kind, if continued 

 through the latter portion of the Tertiary period, would 

 inevitably produce such a limited yet peculiar fauna as is 

 now found to characterise these islands. Minute geo- 

 logical investigation, combined with a more complete 

 knowledge of the existing fauna and flora, will alone 

 enable us to determine how far these suppositions are 

 correct. There is not much doubt, however, that we have 



