118 EVOLUTION 



from internal convulsions, the earth has little serious 

 ground for apprehension. The cause of both earth- 

 quakes and volcanoes is still obscure, but it is at least 

 connected with the intense heat and pressure below 

 the crust. Probably forty to fifty miles of solid rock 

 form the earth's crust. This is a mere egg-shell in 

 comparison with the 8,000 miles of molten matter that 

 is confined and compressed by it, and imagination can 

 easily depict this thin envelope yielding to the pressure 

 below and allowing floods of molten lava to overflow the 

 cities of men. The moon is sometimes referred to as the 

 skeleton at our feast. A dead extinct world (save for 

 some probable traces of vegetation) it seems to say to 

 the earth : " Such as I am, will you also be." Its visible 

 face is studded with some 200,000 crater-like formations 

 that seem to tell of an appalling outpouring of its molten 

 interior upon the surface in some by-gone age. Will the 

 earth sustain some similar epidemic of eruptions in an 

 age to come ? 



The point need not distress us. The smaller size of 

 the moon really involves differences of a very radical 

 character. It is probable that the moon has been too 

 small to retain, by gravitation, an atmosphere round it, 

 and thus been exposed to a fierce bombardment from the 

 heavier meteorites in space. There are astronomers 

 who regard its so-called volcanoes as merely the splashes 

 of large meteorites impinging and liquefying on its face. 

 In any case it is very doubtful if these round formations 

 are volcanic craters. Some of them are sixty miles or 

 more in diameter and only 10,000 to 20,000 feet deep. 

 This is a totally different structure from what we know 

 as a volcano. A distinguished German astronomer, 

 Fauth, who has made a life-study of the moon, believes 

 that its face is one mass of ice, and the "craters" are 

 pits formed by the breaking through of the warmer 



