PICKERING. — LUNAR AND HAWAIIAN PHYSICAL FEATURES COMPARED. 1 
a specimen containing a fossil shell, which was doubtless brought up from the ocean 
bed by the erupted material when the crater was active. A branching system of 
sv 
cracks, none of them exceeding three inches in width, was found in one place. 
The inner slopes of the crater range from 20° to 45°, the outer from 30° to 70". 
Clearly the walls were formerly somewhat higher, and the interior and exterior of the 
crater about on a level. The edge of the rim is extremely sharp in places. The 
material is composed of a hardened volcanic mud or tuff, and while the crater some- 
what resembles numerous of the smaller lunar craterlets, yet their interiors are always 
at a lower level than the exterior plane on which they are situated, and their inner 
slopes are steeper than their outer ones. The crater seems to offer little analogy 
therefore to the formations upon the Moon. 
Cinder cones, c p. 171, form the most numerous class of craters in Hawaii. They 
are found scattered over the summit of Mauna Kea, in the valley between Mauna Kea 
and Mauna Loa, in the interior of Haleakala, along the southern and northwestern 
coasts of Hawaii, and in many other places. A group situated near the summit of 
Mauna Kea is shown in Figure 2. They have all the characteristics of explosive vol- 
canoes like Vesuvius, although their craters are larger in proportion to the height of 
their cones. So far as is known they bear no analogy to anything found upon the 
Moon. 
The third class, or lava craters, on the other hand, present a close resemblance in 
many respects to some of the lunar formations, and we shall therefore describe them 
in detail. The first subdivision, the lava cones, are most strikingly represented by 
Mauna Loa, by far the world's largest volcano. It and Mauna Kea are also our 
highest mountains if we measure in every case from the mountain's base. For the 
Hawaiian volcanoes the base lies 15,000 feet below the level of the sea. Nevertheless, 
the summit crater of Mauna Loa is so large in proportion to its depth that it was 
thought best to select a small lava cone in Haleakala as the typical example of this 
form of crater. This cone is shown in the right foreground of Figure 3, and its sec- 
tion at e on p. 171. The outer slopes of a lava cone are often covered by loose cinders, 
as in the present case, and the inner slopes may be inclined like those of a cinder cone, 
although they are generally much steeper, but if the inner walls are of lava its classi- 
fication is assured. Lava sometimes issues from the summits of these cones, but some- 
times it comes directly out of the ground, as in Kilauea Iki and at Huehue, — no trace 
of a cone being found. 
Lava has not been known within historic times to overflow the summit crater of 
Mauna Loa, but it escapes from just below the summit, outside the crater walls, in 
