THE ORIGIN OF LUNAR VOLCANOES. 107 



planet, are quite in accordance with the above-stated theoreti- 

 cal considerations. 



There is one peculiar feature presented by the cones of the 

 cooling cinder which is especially interesting. The flow of 

 fused cinder from the little crater is at first copious and con- 

 tinuous ; then it diminishes and becomes alternating, by a ris- 

 ing and falling of the fused mass within the cone. Ultimately 

 the flow ceases, and then the inner liquid sinks, more or less, 

 below the level of the orifice. In some cases, where much gas 

 is evolved, this sinking is so considerable as to leave the cone 

 as a mere hollow shell ; the inner liquid having settled down 

 and solidified with a flat or slightly rounded surface, at about 

 the level of the base of the cone, or even lower. These hollow 

 cones were remarkably displayed in some of the cinder of the 

 Henderson iron, and their formation was obviously promoted 

 by the abundant evolution of gas. 



If such hollow cones were formed by the cooling of a mass 

 like that of the Moon, they would ultimately and gradually 

 subside by their own weight. But how would they yield ? 

 Obviously, by a gradual hinge-like bending at the base toward 

 the axis of the cone. This would occur with or without fract- 

 ure, according to the degree of viscosity of the crust and the 

 amount of inclination. But the sides of the hollow-cone shell, 

 in falling toward the axis, would be crushing into smaller cir- 

 cumferences. "What would result from this ? I think it must 

 be the formation of fissures, extending, for the most part, 

 radially from the crater toward the base, and a crumpling up 

 of the shell of the cone by foldings in the same direction. 

 Am I venturing too far in suggesting that in this manner may 

 have been formed the mysterious rays and rills that extend so 

 abundantly from several of the lunar craters ? 



The upturned edges or walls of the broken crust, and the 

 chasms necessarily gaping between them, appear to satisfy the 

 peculiar phenomena of reflection which these rays present. 

 These edges of the fractured crust would lean toward each 

 other, and form angular chasms ; while the foldings of the 

 crust itself would form long concave troughs, extending radially 

 from the crater. 



These, when illuminated by rays falling upon them in the 

 direction of the line of vision, must reflect more light toward 

 the spectator than does the general convex lunar surface, and 

 thus they become especially visible at the full Moon. 



Such foldings and fractures would occur after the subsidence 



