DISTRIBUTION OF BIRDS IN TIME AND SPACE. 199 



The imaginary line drawn through the sea to 

 serve as a boundary between Bali in the east, and 

 Lombok in the west, with the islands belonging 

 to each, was called ''Wallace's line," in honour 

 of Mr Alfred Eussel Wallace, who first pointed 

 out the significance of this barrier of deep 

 water. 



So far, all the islands of which we have spoken 

 have been, at some time or another, parts of the 

 nearest mainland. The fauna and flora represent 

 more or less the fauna and flora of the mainland 

 at the time when this particular portion became 

 isolated. The rocks will be found to be stratified, 

 and to agree in character with those of the main- 

 land. 



Other islands there are, however, which are 

 of quite diflerent origin. They are known as 

 "Oceanic," as opposed to those just described 

 which are called "Continental." An Oceanic 

 island is either of volcanic or coral origin. At 

 no time, therefore, has it ever formed part of 

 the mainland. Its fauna and flora are peculiar, 

 being derived from the nearest mainland, and 

 carried thither by the wind, or from the flotsam 

 and jetsam of the sea. The sea contributes 

 such vegetable seeds as have hard shells, im- 

 permeable to salt water. These are cast up by 

 the waves and often manage to find a root-hold 

 on the shore ; and such small mammalia as may 

 have been conveyed on trunks of trees brought 

 down from the nearest mainland by flood ; or 

 birds, as may have flown thither from some 

 other island or continent. 



The wind brings seeds of plants and 



