324 SAMOAN ISLANDS. 
of thin layers closely adhering. ‘They break with a resinous lustre, 
and when fresh and moist may be cut with a knife; but on drying 
they become nearly as hard as apatite. In two analyses by Professor 
B. Silliman, Jr., their constitution was ascertained to be as follows :* 
Sp. gr. 1°894. Sp. gr. 1°689—1°813. 
Silica - - - - 35°138 31°252 
Alumina = : - 31°950 37°208 
Water : : - 30°800 30°450 
Magnesia - - - 1-050 0-061 
Carbonate of lime - 1-210 0-008 
Fluorine - - - trace. trace. 
Soda - - - - trace. 0:062 
100°148 99°041 
They are essentially hydrous silicates of alumina, and have resulted 
from the decomposition of the lavas that overlie the cavern. 
Mr. Peale found a passage leading from the place where he entered 
the cavern to the northeastward, which he supposed to be the con- 
tinuation of the cavern up the mountain. He traced it along for five 
hundred feet, and found no termination. 
Besides the volcanic region of the western district here described, 
there appears to have been an eruption of the same age near Laulii, 
within the central district, intruding there among the older rocks. 
Crossing a low ridge one hundred or one hundred and fifty feet high, 
just east of the place near the shores, I passed over large quantities of 
* « Alone in a close tube it gives off water copiously, which is neutral to georgina paper. 
The powder by heating becomes gray, but does not cohere. Alone in the platinum forceps 
it decrepitates, loses water, becoming opaque, but does not fuse. 
“With carbonate of soda it forms a bead, transparent when hot and opaque when cold. 
With borax it yields a colourless transparent bead, alike in colour both when hot and 
cold. 
“Tn nitric or hydrochloric acids it gelatinizes and dissolves, leaving a portion of silica ; 
traces of chlorine and sulphuric acid were detected in the nitric solution. Traces only 
of lime, magnesia, and alkaline chlorids were detected by the usual tests, Ammonia 
produces a copious gelatinous precipitate of hydrate of alumina in the solution of the 
mineral. Lime-water throws down from the neutral solution a small precipitate, which, 
when collected and decomposed by sulphuric acid in a platinum vessel, distinctly etched 
a glass plate prepared with wax, thus proving the presence of a minute portion of 
fluorine. 
“The partial decomposition of the mineral rendered its composition uncertain, as the 
water of constitution varied nearly ten per cent. in different portions, and the silica and 
alumina five or six.”"—B. S., Jr. 
