268 James Nasmyth, Esq., on the Structure of the 



solidation and alternate contraction of the crust and interior 

 of the earth or moon, both of which planets appear to have 

 originally been in a molten condition. 



After drawing attention to the vast number and magnitude 

 of crater-formed mountains with which every portion of the 

 moon's surface appears to be covered, Mr Nasmyth proceeded 

 to give the reasons for the conclusion that these crater- 

 formed mountains are really the craters of extinct lunar vol- 

 canoes ; pointing out the frequent occurrence of the central 

 cone, the result of the last eruptive efforts of an expiring vol- 

 cano, a feature familiar to all those who have observed vol- 

 canic craters on the earth's surface. This central cone Mr 

 Nasmyth shewed to exist in the majority of the lunar craters, 

 and thereby drew the conclusion that they were the result of 

 the same kind of action which has produced craters on the 

 volcanoes of the earth. 



The cause of the vast numbers of such volcanic mountains 

 with which the lunar surface is bespattered was next con- 

 sidered, and traced to the rapid consolidation and construc- 

 tion of the crust of the moon, whose mass or bulk being only 

 ^\th of that of the earth, while its surface is the iVth, has, 

 in consequence of these proportions, radiating or heat dis- 

 pensing surface four times greater than that of the earth in 

 relation to its bulk. From this simple geometrical considera- 

 tion Mr Nasmyth explained how it was that, by the rapid 

 cooling and collapse of the crust of the moon on its molten 

 interior, the fluid matter under the solid crust was by this 

 " hide binding" action forced to find an escape tlp:*ough the 

 superincumbent solid crust and come forth in the great vol- 

 canic actions which in some remote period of time have 

 covered its surface with those myriads of craters and volcanic 

 features that give to its surface its remarkable character. 



The cause of the vast magnitude of the lunar craters was 

 next alluded to, and assigned, as in the former case, to the 

 rapid and energetic collapse of the moon's crust on its yet 

 molten interior. The action as regards the wide dispersion 

 of the ejected matter was enhanced by the lightness of the 

 erupted matter, the force of gravity which gives the quality 

 of rceiyht to matter on the moon as on the earth being very 



