348 CORALS AND CORAL ISLANDS. 
not prepared for a full answer to this inquiry; for it would de. 
mand a thorough knowledge of the shores, as well as of the cur- 
rents, and of the former and present condition of volcanic fires. 
From personal observation we may reply satisfactorily, as far as 
regards part of the southern half of the east coast of Su- 
matra. This coast is low, and sandy, or muddy, and thus af: 
fords the most unfavorable place for zodphytes. A strong 
current sweeps through the Straits of Banka, which keeps the 
water muddy, and the shores in constant change. The same 
cause may operate on the coasts of other islands, but we can- 
not say to what extent. 
The East Indies have been remarkable for their volcanoes, 
exceeding, for the area, everv other part of the world; and this 
fact must. have had influence on the formation of coral reefs, 
though there are not data for fixing the extent of the influence. - 
Of the thousand vents which have been in action, several still 
make themselves felt over wide areas. The Sooloo Islands are 
about one hundred in number, and nearly all are pointed with 
voleanic cones, and while some have the broken declivities that 
are marks of age, others have regular slopes, as if but just now 
extinguished; a dozen of these cones may sometimes be seen 
on a single island. These volcanic peaks often rise out of the 
sea, as if their formation had begun with a submarine erup- 
tion. Ina region so extensively and so recently igneous, the 
coral polyps would have found little chance for growth, until 
volcanic action had become comparatively quiet, and deluges 
of hot water ceased. There appears, therefore, to be some 
reason for the fact that the reefs are small, and have seldom 
reached the surface. The Sooloo Sea is but one of the volcan- 
ic centers in these seas. Java, several of the Philippines, and 
other islands south of these last, with the northern shore of 
New Guinea, make up a wide region of fires, and it cannot be 
