272 HAWAIIAN ISLANDS. 
large size: one, the first entered by the author, not far from Koloa, 
was ten feet high, twenty feet broad, and fifty long. The layer which 
covered the cavity was about five feet thick, both over the cavity 
and elsewhere. ‘The roof was very rough, though not stalactitic. 
Caverns of this kind, upon the coast, afford water-scenes of a striking 
character. The waves of the wide Pacific driving over the black 
rocks, into dark recesses, and rising in copious jets or dashing into 
foam, afford majestic sights wherever seen about these volcanic islands; 
and some of the spout-holes of Koloa are unusually grand. 
The rock of the region is a ferruginous basalt of a black or brown- 
ish-black colour, and generally has a glistening lustre. Excepting 
sparsely disseminated grains of chrysolite, there are no traces of 
crystallization. In other words, the rock is the same as that of Ka- 
neohe Point, the craters near Diamond Hill, and other parts of the 
islands. The lava is more or less cellular, but is very compact 
between the cellules. In some places it is columnar. Along the 
banks of a small stream that runs through the village of Koloa, there 
are well-defined prisms of five, six, or seven sides, and they form a 
neat polygonal pavement, or stand in columnar walls. The columns 
seldom exceed eighteen inches in diameter. Horizontal fractures 
occur at regular intervals, but the plane of fracture is flat instead of 
convex. In these pavements, the rock immediately adjoining the 
fissures or lines of fracture, is often harder than that within, and 
gradual abrasion wears the inner parts, leaving an elevated line along 
the fissures. ‘This superior hardness has probably arisen from infil- 
tration subsequent to the formation of the fissures; gases from below, 
usually decompose instead of giving increased hardness. 
The number of volcanic hills is five, and among them, one contains 
two craters, and another three craters, as shown in the preceding map. 
With one exception, they are low, with a rounded contour and barren 
earthy sides, looking as if made of dark-coloured brickdust. The one 
exception, called the Old Crater, is represented to the left in the above 
sketch. 
