276 Reviews — Nasmyth and Carpenter on the Moon. 



violent ejection of the matter underlying the solidified crust of the 

 moon/' by a force derived "from the expansion of a solidifying 

 substratum, withovt having recourse to aqueous or gaseous sources 

 of eruptive poiver," — a process which does not appear very intel- 

 ligible. It is undeniable that the production of volcanic mountains, 

 and still more of craters, upon our earth, is due to the eruptive forces 

 of some elastic vapour or gas (chiefly, if not solely, steam). If, 

 therefore, we are to believe in any analogy between terrestrial and 

 lunar volcanic action, we cannot dispense with the influence of the 

 outburst of elastic vapour from the surface of the moon in the pro- 

 duction of her craters. I cannot indeed conceive the violent ejection 

 and dispersion of fragmentary or of liquid matter to horizontal 

 distances of many miles — which is required in the theory of these 

 authors — by the mere escape of liquid from a vent, unaccompanied 

 by any explosive force. The phenomena of Kilauea perhaps offer 

 the nearest approach to an example of inexplosive volcanic action. 

 And the authors of the work before me modestly express some doubt 

 whether Dana's reference of the formation of the lunar craters to a 

 similar process, i.e. to the mere circular spreading of heat from the 

 centre of an ebullient lava surface, be not more plausible than their 

 own theory. But Kilauea is a very exceptional case among terres- 

 trial volcanos. Its crater is a lateral aperture or well, kept open by 

 the rather tranquil boiling up of what may be called a spring of lava 

 in its centre. It lies low down on the flank of a dome-shaped 

 volcanic mountain (Mauna Loa), which rises 10,000 feet above it, 

 and is frequently in eruption, so that the column of liquid lava in 

 this main vent may be supposed to supply that which wells up in 

 the lower branch of the syphon. There is no bank or annular 

 rampart on the outside of its inner clifi's. On the whole Kilauea 

 bears little or no resemblance to the normal type of lunar craters. 



Nevertheless the peculiarities of these craters do seem to me to 

 suggest some deviation from the ordinary explosive action of terres- 

 trial volcanos, to which the formation of the vast crater-rings of 

 Madeira, Teneriffe, St. Helena, Santorini, etc., are clearly attributable. 

 These are, unquestionably, as I have called them, after Mr. Darwin, 

 " the basal wrecks or remnants " of great volcanic mountains, the 

 summits and central parts of which have been blown into the air 

 by continuous explosive outbursts of steam. That they are so is 

 proved by the outward quaquaversal dip of repeated beds of solid 

 lavas and their conglomerates, of which these remnants are always 

 composed. In the moon, on the other hand, as I have already said, 

 there does not exist a single mountain of the kind, and it is not 

 likely, therefore, that its numerous craters ever possessed this 

 character. Our globe, however, presents us with examples of 

 craters of another class, — both large and small, and some of a 

 magnitude almost rivalling in area the largest of the lunar craters, — 

 I mean those craters that have resulted from single eruptions upon 

 fresh points of the earth's surface, and especially the crater-lakes of 

 common occurrence in many volcanic districts — saucer-like hollows 

 surrounded by banks of fragmentary matter, sometimes breached at 



