250 HAWATIAN ISLANDS. 
Oahu. We barely allude to the scoria beds or deposits of the Pali, at 
the head of the Nuuanu Valley, as apparently among the most recent 
indications of eruption in Oahu, though no distinct crater or centre 
of eruption was made out. ‘The scoria and pitchstone cinders are 
loosely aggregated, and form a deposit of large extent. 
3. WESTERN DIVISION OF OAHU. 
The mountains of the western division of the island, are broken 
irregularly into ridges and peaks, with deep valleys and steep slopes. 
The outline is not strikingly uneven, yet runs up into several elevated 
summits, of which Kaala is the highest. As seen from the westward, 
this peak appears to have a table summit; but from other directions 
it is pointed. ‘To the south of Kaala, there is a gap in the ridge, where 
a path crosses to the plains of Waianae, only fourteen hundred feet 
above the sea; farther south, there is another pass, at an elevation of 
about sixteen hundred feet. 
These mountains are very abrupt towards the southwest. They 
have, in general, a bold mural front, around the Waianae plains, and 
are deeply furrowed or fluted, and shouldered up by narrow buttresses, 
much like the Kaneohe side of the eastern range. But tothe eastward 
and northward of east, the slopes are gradual, and they pass into the 
gentle declivities of the dividing plain. 
The rocks of these western mountains are mostly a gray basalt or 
graystone, and are often somewhat cellular. They are frequently 
much porphyritic, small tabular feldspathic crystals being thickly dis- 
seminated. Some of the isolated ridges on the Waianae plains (see 
map), consist of a kind of clinkstone porphyry, allied to the clink- 
stone of Hawaii and Maui. The colours presented are various, as dull 
brownish-black, purplish, bluish-gray, and grayish-white; and the 
compact base is finely speckled, in most parts, with points of feldspar. 
On decomposition it becomes white, and so soft that it may be used 
like chalk. Conglomerate layers are abundant in these mountains. 
Some hills at the foot of the precipice, at the pass south of Kaala, 
consist of a coarse volcanic breccia, firmly cemented, in which some 
of the masses of scoria and lava are several feet through. ‘The hills 
are three to six hundred feet high, and are imperfectly divided into 
thick layers. ‘They appear to have been formed soon after an erup- 
tion of lava, of the angular masses of volcanic rock then ejected, and 
