244 | HAWAIIAN ISLANDS. 
obliquely truncate at top, owing to the action of the trade-winds at- 
tending its formation, and not to degradation. The southwestern side 
VIEW OF KOKO HEAD CRATERS, FROM THE EAST. 
is the highest, being by my estimate seven hundred feet in elevation. 
The cavity within is nearly as deep as the height of the cone, the in- 
terior having apparently been worn out by water, for which there is 
an exit by a deep gap on the northern side. 
The southern hill is about three hundred and fifty feet high. It 
forms a segment of a circle around a small circular cove, towards 
which the slopes incline. ‘This cove has evidently been a centre of 
eruption ; but it was possibly subordinate to a larger vent, which has 
disappeared beneath the waves, as may be inferred from the extent 
and position of the ridge, and the cliff which exhibits a section of this 
ridge. The north side is much the lowest, (but eighty feet,) for the 
same reason as in the case of the crater above mentioned. 
Upon the inner slopes of this hill, not far above the cove, there is a 
more recently formed crater, about two hundred and fifty yards across. 
The layers of tufa dip in various directions, owing to the number of 
combined vents which have here been in action. In the highest part 
of the ridge they lap over it, dipping outward towards the west, and 
inward towards the east, as in the other cones examined. But near 
the subordinate vents, the dip corresponds, according to the same prin- 
ciple, with the position of these vents. The layers around the small 
crater in the side of the ridge lie over the others, and are of most recent 
date. About half way up the ascent to this small crater, there is the 
only bed of lava I saw about this region; and it was evident that it 
had flowed from this vent. 
The tufa is very similar to that of Diamond Hill, and like that is 
interlaminated with lime. The layers are often less than a line thick 
and very distinct. One hundred and fifty feet above the sea, I found 
fragments of coral limestone and shells imbedded in the tufa. In some 
parts large fragments of rock were also included. Some varieties of 
the tufa have a greenish tint from the proportion of chrysolite, and the 
