384 
ISLAND LIFE. 
[part it. 
and may leave the ancient fauna in a very fragmentary state ; 
while subsequent elevations may have brought it so near to the 
continent that some immigration even of mammalia may have 
taken place. If these elevations and subsidences occurred several 
times over, though never to such an extent as again to unite the 
island with the continent, it is evident that a very complex 
result might be produced ; for besides the relics of the ancient 
fauna, we might have successive immigrations from surrounding 
lands reaching down to the era of existing species. Bearing in 
mind these possible changes, we shall generally be able to arrive 
at a fair conjectural solution of the phenomena of distribution 
presented by these ancient islands. 
Undoubtedly the most interesting of such islands, and that 
which exhibits their chief peculiarities in the greatest perfec- 
tion, is Madagascar, and we shall therefore enter somewhat fully 
into its biological and physical history. 
Physical features of Madagascar . — This great island is situated 
about 250 miles from the east coast of Africa, and extends 
from 12° to 25|-° S. Lat. It is almost exactly 1,000 miles 
long, with an extreme width of 360 and an average width of 
more than 260 miles. A lofty granitic plateau, from eighty to 
160 miles wide and from 3,000 to 5,000 feet high, occupies its 
central portion, on which rise peaks and domes of basalt and 
granite to a height of nearly 9,000 feet; and there are also 
numerous extinct volcanic cones and craters. All round the 
island, but especially developed on the south and west, are 
plains of a few hundred feet elevation, formed of rocks which 
are shown by their fossils to be of Jurassic age, or at all events 
to belong to somewhere near the middle portion of the Secondary 
period. The higher granitic plateau consists of bare undulating 
moors, while the lower Secondary plains are more or less wooded ; 
and there is here also a continuous belt of dense forest, varying 
from six or eight to fifty miles wide, encircling the whole island, 
usually at about thirty miles distance from the coast but in the 
north-east coming down to the sea-shore. 
The sea around Madagascar, when the shallow bank on which it 
stands is passed, is generally deep. This 100-fathom bank is only 
from one to three miles wide on the east side, but on the west 
