URS GER RD ES Ud or 
J. D. Dana on the Volcanoes of the Moon. 347 
: still distinct ; for if spread-out at a height of five hundred feet 
above the bottom, they would still in many instances be more 
than ten thousand feet below the summit, and far below too the 
tops of interior peaks. : 
- As there is little or no water in the moon to aid voleanic action, 
sulphur has probably played an important part im its igneous 
changes ; for this is not only a prevalent means of igneous. ope- 
tations on our globe, but occurs in meteoric stones, pyrites being 
one of their common constituents. We may therefore believe 
that, wherever there is action in the moon, sulphur and any other 
Vaporizable material present, are constantly escaping either as 
simple vapor or in some gaseous combination, and forming a very 
low covering over certain portions. 
As we have observed, the existence of actual volcanic eruption 
in the moon. is still doubtful, and we must look to new facts to 
_ Settle the point. . But we cannot doubt that the surface in former 
periods has been everywhere in violent action, and that its pools 
of fire were once measured by scores of miles instead of by hun- 
dreds of yards, as with our existing voleanoes. And many of these 
immense basins remain still open for examination, presenting 
indications of the various changes which accompanied the grad- 
ual decrease of igneous action during the cooling in progress. A 
Map of the moon, if there is any truth in these views, should 
be in every geological lecture room; for no where can, we have 
& more complete or more magnificent illustration of voleanic ope- 
tations. Our own. sublimest voleanoes would rank among the 
smaller lunar eminences; and our Etnas are but spitting furnaces. 
In continuation, I would ask attention to some thoughts bear- 
ing on our own planet, which are suggested by this study of the 
Moon’s surface, i 
L If the earth was once a melted globe, it must have 
through the same phases as the moon, with this very ¢mportant 
difference, that the whole surface during its progress was subject 
to the denuding action of waters, and from the first had valleys 
_ and sedimentary rocks in progress. It must have had originally 
its boiling pools of vast extent; which as the action decreased in 
lence would more or less gradually contract. Are there any 
Temains of these great craters? Or have they disappeared by a 
decrease in the voleanic action and thus graduated into existing 
