312 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 zoophytes. 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, every 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 

 volcanic 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. In a 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 clusters 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 



