I 
156 PICKERING. — LUNAR AND HAWAIIAN PHYSICAL FEATURES COMPARED. 
o 
enormous quantities, especially upon the northeastern side. The vast bulk of the 
mountain seems to have been built up largely from these emissions, and the same is 
true also of Mt. Etna in Sicily. It is characteristic of these mountains that their 
slopes are much more gentle than those of cinder cones, and this is especially true 
of Mauna Loa, Figure 4. The summit of this mountain is 13,675 feet in elevation. 
The view was taken from the north, and represents the upper 7000 feet of the moun- 
tain. The summit is very difficult of access on account of the exceedingly rough 
nature of the ground, the total absence of water, and on account of its flatness of 
distance of the summit from a base of supplies. It is probably best reached 
from the Kona, or western side, by way of Kealakekua Bay. 
The slopes of Etna are heavily buttressed by ridges, formed each of a separate 
lava stream, which has flowed from the small lava cones upon the flanks of the 
mountain. This structure is also well shown in the lunar crater Bullialdus, Figure 5. 
The diameter of this crater is 38 miles. Since these streams sometimes cross one 
another, leaving diamond-shaped hollows between them, it is obvious that the 
formation cannot be due to the grooving of a smooth surface by erosion, but must 
really be formed by projecting ridges. We shall refer again to this matter in con- 
nection with Clavius and Kilauea Iki. We thus have indirect evidence of the exist- 
ence of lava cones upon the Moon, as the source of these streams. 
Until recently this was all the evidence we had. The tall volcanic cone with the 
comparatively minute crater at its summit, so characteristic of the typical terrestrial 
volcano, was supposed to be absent from the Moon. In the terrestrial volcano the 
floor of the crater is always higher than its base ; on the Moon the reverse is true. 
A recent examination of a lunar photograph taken at the Yerkes Observatory by 
Professor Ritchey has shown, however, that the terrestrial type of volcano is not 
wholly absent from the Moon. Craters of this type have not been found before, 
merely because, like those on the Earth, they are very small. Figure 6 represents 
the two craters Kies and Mercator. Between them is seen a comparatively small 
cone with a minute crater upon its summit. It proves to be nine miles in diameter 
at its base, and 2000 feet in height, while the crater itself measures half a mile in 
diameter. For purposes of comparison we may say that the diameter of the base 
of Vesuvius, including Monte Somma, is eight miles, and its height 4000 feet. The 
diameter of its crater, which varies with every eruption, rarely exceeds one quarter of 
a mile, and is sometimes but a few hundred feet. The mean angle of the slope of Vesu- 
vius is 10.7, that of Etna 7.6, of Mauna Loa 5J, and of the lunar cone IS. Vesuvius 
is partly a lava and partly a cinder cone, which accounts for its steepness. If it were 
