OAHU. 239 
a light gray colour, and is speckled with a white soda feldspar which 
constitutes the greater part of the whole: but besides, there are dark 
green points of impure augite. The rock is exceedingly compact, 
without a trace of a cellule, and it breaks into coarse plates or slabs 
owing to a lamellar structure. 
These solid layers alternate at times with conglomerates and tufas. 
Many of the conglomerates are beds of rounded stones and gravel, 
of the same material as the mountain. Others are compacted beds of 
basaltic earth, and have a tufa character. The material in a few 
places consists of true volcanic scoria and cinders, the former twisted 
and ropy, and the latter looking like comminuted pitchstone; and the 
whole is so loosely aggregated as to crumble in the hands. 
The alternation of the solid and conglomerate layers may be seen 
in many places. At the Pali, it is well exhibited, and in some por- 
tions of this mountain wall the latter constitute a large proportion of 
the height. In many of the gorges near Ewa the same is shown. A 
section exposed near the Ewa church, contains a series of layers com- 
posed of rounded stones and earth, loosely compacted. ‘There are 
twelve feet of basaltic earth between two layers of the loose conglome- 
rate, and another tufa layer overlies the upper conglomerate, about 
sixty feet above the sea. The conglomerate layers are very irregular, 
graduating frequently into the finer kinds, and forming isolated beds. 
At Waipeo, where is presented another section of the same plain, 
there is a clayey deposit of a tufa character, three or four feet thick. It 
hes thirty-five feet above the sea, and below twenty-five feet of the 
soft layers of basaltic earth and pebbles. 
At the foot of the mountains near Honolulu, and farther east, the 
layers are mostly basaltic lava, with rarely any of the conglomerate 
intervening. They have in general nearly the ragged appearance of 
recent lava, though not scoriaceous. ‘The under surface of the black 
layers is rough and uneven. Many a cavern opens upon the sides of 
the valleys, some of which are the habitations of the natives, and 
others their burial places. Like those of Hawaii, they are merely 
vacant spaces left beneath the streams of rock as they flowed along at 
some former period. In one of them, | made my way over scattered 
bones and skulls for one hundred yards, through which distance it 
varied in height from six feet to three and a half. Beyond, it became 
too low for farther exploration. The roof was rough, and in some 
parts had a thin calcareous coating. 
The basaltic rocks present frequent traces of a columnar struc- 
