572 H. B. GTJPPY ON THE RECENT 



was attained, when I descended into a deep valley and followed up the bed of 

 a large stream, which finally emerged from a cavern of considerable dimensions 

 in the face of a hill of coral limestone. This cavern was first visited by the 

 Rev. Mr Penny of the Melanesian Mission, and was subsequently explored 

 by Bishop Selwyn, to whom I was indebted for the opportunity of examining 

 it. The interior, the entrance to which is between 60 and 70 feet in height, 

 presents the usual features of these subterranean cavities. A series of lofty 

 chambers, connected by narrow passages and containing numerous stalactitic 

 and stalagmitic columns in all stages of formation, some of them between 

 1 and 2 feet in diameter — such is the character of this cavern which Bishop 

 Selwyn found to be about 750 yards in length. I emerged from the farthest 

 mouth into the bottom of a deep valley, across which the coral limestone hill 

 lies as a dam through which the stream has found its way. In the bed of the 

 stream, as it follows its subterranean course, there are numerous blocks and 

 pebbles of a dark crystalline volcanic rock and of a marley rock, of which I 

 Avas unable to find the parent rocks in the valley above. They are probably 

 traversed by the stream in its passage through the hill, where they would be 

 concealed from view by the stalagmitic and stalactitic deposits. The marl 

 presumably represents the immediate foundation of the limestone, and will be 

 found to cover the crystalline volcanic rock. From the presence of these rocks 

 in the bed of the stream as it flows through the caverns, I suspect that these 

 subterranean passages traverse the base of the limestone ; and on this supposi- 

 tion the thickness of this coral limestone would be not greater than the height 

 of the hill which is pierced by the stream, i.e., about 150 feet. 



The general conclusion that I formed of the structure of this eastern island 

 of the Florida Sub-group was, that the calcareous rocks were merely superficial 

 formations encrusting a nucleus of volcanic rocks which has been occasionally 

 exposed to view by the denuding forces. 



The Classification or The Solomon Island Recent Formations. 



These rocks may be grouped into two chief classes, according to the pro- 

 portion of volcanic debris they contain. 



The First Class comprises those rocks which, being largely composed of 

 such volcanic debris mixed with the tests of Foraminifera, Pteropods, and 

 other Molluscs, have a composition very similar to that of the volcanic muds 

 at present forming around oceanic volcanic islands in the Pacific. These rocks 

 contain both pelagic and bottom forms of Foraminifera, lists of which have 

 been given in the^ previous pages. The soft rock, resembling a deep-sea clay, 

 which underlies the elevated reef-mass at Santa Anna, may be referred to this 

 principal division of the rocks ; but, as shown in the description on page 558, 



