250 
GILBERT. 
Eventually the reissue of lava builds a new cone inside the 
great crater, and this cone, which always carries a crater 
at top, may grow so as to bury completely the wreck of the 
great explosion. 
With the forms resulting from this process, or alternation 
of processes, the lunar craters have little in common. Ninety- 
nine times in one hundred the bottom of the lunar crater lies 
lower than the outer plain; ninety- 
nine times in a hundred the bottom 
of the Vesuvian crater lies higher 
than the outer plain. Ordinarily the 
inner height of the lunar crater rim 
is more than double its outer height; 
ordinarily the outer height of the 
Vesuvian crater rim is more than 
double its inner height. The lunar 
crater is sunk in the lunar plain ; the Vesuvian is perched 
on a mountain top. The rim of the Vesuvian crater is not 
developed, like the lunar, into a complex wreath, but slopes 
outward and inward from a simple 
crest-line. If the Vesuvian crater has 
a central hill, that hill bears a crater 
at summit and is a miniature repro¬ 
duction of the outer cone; the central 
hill of the lunar crater is entire, and 
is distinct in topographic character 
from the circling rim. The inner 
cone of a Vesuvian volcano may rise 
far higher than the outer; the central hill of the lunar 
crater never rises to the height of the rim and rarely 
to the level of the outer plain. The smooth inner plain 
characteristic of so many lunar craters is either rare or un¬ 
known in craters of Vesuvian type. Thus, through the 
expression of every feature the lunar crater emphatically 
denies kinship with the ordinary volcanoes of the earth. 
If it was once nourished by a vital fluid, that fluid was not 
the steam-gorged lava of Vesuvius and Etna. 
Fig. 7.— Crater of Vesuvian 
type, with central cone. Fea¬ 
tures due to erosion are 
omitted. 
Fig. 6.—Crater of Vesuvian 
type, without central cone. 
Features due to erosion are 
omitted. 
