PICKERING. LUNAR AND HAWAIIAN TIlVSICAL FEATURES COMPARED. 1G1 
two large craters there represented, named Schickard and Phocylides, both present a 
form similar to the crater rings of Halemanmau. The chief one, Schickard, measures 
134 miles in diameter. All of the larger craters on the Moon are of this typo. 
When seen towards the centre of the disc, however, their depth appears by an optical 
illusion greatly exaggerated. Thus Clavius, the largest crater shown in Figure 1G 
measures 143 miles in diameter, and judging by appearances only might he 15 to 20 
miles in depth. Its depth actually measures two and a half mile.-, or a) tout the same 
as the diameter of one of the most minute craterlets visible in its interior. The slope 
of its eastern inner wall is about 10°. 
There is another crater known as Wargentin, lying between Schickard and 
Phocylides and the limb, Figure 14. It is not shown in the photograph because it is 
a very difficult object. This is not on account of its size, since it measures fifty-four 
miles in diameter, but because it has no interior depression. In this respect it has 
heretofore been thought to be unique upon the Moon. That such is not the case, 
however, an inspection of Figure 32 will show. Near the upper edge of the figure 
a large low nameless crater is to be seen whose interior is obviously at a greater 
elevation than its exterior, although the difference is not as great as in the case of 
Wargentin. It measures about fifteen miles in diameter. In each of these case 
the lava passage leading to the interior of the crater evidently became choked while 
the crater was still brimful of molten matter, thus preventing the withdrawal of the 
lava, and preserving the crater as a permanent illustration of the method by which 
these formations are produced. 
The outside height of the crater rings in Halemaumau rarely exceeds 15 to 25 feet. 
The inside height is constantly varying with the fluctuating level of the surface 
of the lava lake. When the outside height becomes too great to withstand the 
•essure, the rim gives way, and the lava breaks through and floods the 
rounding regions. By means of this successive building up and flooding, the whole 
P 
region around Halemaumau was elevated, until the walls became too high and too 
thick for the floods to escape over or through them. The pit at this time measured a 
mile by a mile and a half, and was 700 feet in depth. Since the lava could not 
now overflow the rim, it escaped by subterranean passages, and thus flooded the 
other portions of the floor of Kilauea. A. J. S., CII, 454. 
It is doubtful if the walls of the pit were raised exclusively by the process thus 
explained by Mr. Coan. It is probable that the whole of this portion of the floor 
was also elevated as one piece by the pressure of the subterranean lava, as occurred 
in the later eruptions. 
n 
