238 HAWATIAN ISLANDS. 
A. Geological Structure and Constitution of the Eastern Mountains 
and Lateral Craters. 
a. Mountains. 
Structure—The many valleys of the south and west are deep 
sections exhibiting the interior structure of the mountains. Yet the 
declivities are so enveloped in foliage and earth, even where steepest, 
that only general facts are open to view. The stratified structure 
of the whole is, however, apparent in every part, from the foot of the 
hills to the summit, black stripes of rock in many places showing them- 
selves through the verdure. ‘The dip of the layers is uniformly away 
from the crest to the shores, until approaching the dividing plain, where 
it becomes more southwesterly, and beyond this to the northward, it 
is even westerly. In other words, the layers have the slope that cha- 
racterizes the mountain as a whole, declining towards the circumfe- 
rence of a circle that might be described through Koko Head, Dia- 
mond Hill and the dividing plain. Farther to the northwest, the 
layers slope northwest, following in this way nearly the points of the 
compass. In the lofty wall which faces the north, only the edges of 
layers are exposed. 
The dip is small, being but five to eight or ten degrees: and it is as 
uniform in amount as in direction; for there are no tiltings—no anticli- 
nal and synclinal valleys. Every gorge is alike on its opposite sides as 
far as they can be studied. Such simplicity of arrangement affords 
little material for particular description. 
Rocks.—The material of the layers is mostly a black or brownish- 
black basaltic lava, containing chrysolite. It is a heavy rock, more 
or less cellular, like much of the basaltic lava of Hawaii and Maui, 
and sometimes has the ropy surface of a recent eruption. When the 
cellules are few, as is commonly the case, it breaks with a nearly 
smooth or splintery surface, and a slightly glistening lustre. Except- 
ing the chrysolite, no crystals or grains of any kind are to be detected. 
This black variety passes also into grayish or bluish rocks of similar 
constitution, but containing less iron. They vary in compactness and 
in the proportion of chrysolite. 
These again graduate into a clinkstone like that of Hawaii. Ata 
locality about three miles east of Honolulu, a variety of this rock has 
