278 Reviews — Nasmyth and Carpenter on the Moon. 



universally possess. The innumerable smaller craters are undeni- 

 ably of the ordinary terrestrial type, and from their position may 

 be considered as subsidiary or parasitic to the larger, fey which I 

 mean all above three or four miles in diameter. These last, though 

 ranged in strings or clusters, in which each nearly or quite touches 

 another, yet do not cross or (except in the rarest instances) overlap. 

 No more complete proof could be afforded of their simultaneous 

 origin, as well as of their having been mainly produced by that 

 horizontal dispersive force urging concentric waves and jets of 

 matter from the central vent, to which I have ascribed them. Had 

 these several craters been consecutively produced, it is difficult to 

 conceive that the later-formed should not have often covered or 

 overlapped the earlier- So also, if the explosive action had been 

 chiefly vertical rather than horizontal the fragmentary masses thrown 

 up by one vent would often have been mingled with those of its 

 neighbours in irregular ridges, in lieu of the extremely regular 

 rings we see. The next step in the process to the formation of 

 the craters seems to have been, as I have said, the tranquil 

 welling-up from beneath, through theii* central vent-s, of a pro- 

 digious abundance of liquid lava, filling them up more or less 

 completely, and often causing breaches in the encircling walls, 

 through which floods of lava escaped and sjDread, either in rugged 

 streams, or more even sheets, over the surrounding plains. This is 

 known to be a very common if not universal circumstance among 

 terrestrial volcanos. And we need not hesitate to believe in its 

 occurrence in those of the moon, because of the vastness of the 

 surfaces apparently covered by its lava-flows. While I am writ- 

 ing I see a report by Professor Leeonte describing the great lava- 

 flood of California, Oregon, and Washington, as having, during 

 or after the Miocene period, deluged a tract of between 200,000 

 and 300,000 square miles, its average thickness being probably 

 2000 feet! He believes this vast amount of liquid matter "to 

 have been squeezed out from beneath through fissures in the super- 

 ficial rocks, by horizontal and vertical pressure." The area thus 

 covered exceeds any of the great plains of the moon — even the so- 

 called seas. Subsequently to the occurrence of these lava-floods, 

 their rapidly consolidating surface seems to have been fissured by 

 cracks sometimes radiating from a principal crater like those in 

 starred glass, sometimes independent or irregularly branching from 

 one another ; the former appearing to have given vent to partial out- 

 flows of lava through their whole length, producing the white streaks 

 already noticed ; the latter to some of the small subsidiary cones and 

 craters already alluded to. Vast numbers of these likewise were 

 thrown up on the intervening plains, both within and without the 

 larger crater-rings, and many upon the ramparts themselves. At 

 or about the same time the mountains appear to have risen by 

 exudation as the last product of their central vents. While in some 

 rare cases ranges of similar excrescences (one called the Apennines, 

 of considerable size and height) were produced in the same way 

 from fissures across the plains. Finally, the further consolidation 



