433 Mr. R. P. Greg on the Lunar Origin of Aerolites. 



point to the immense internal force required to elevate the 

 melted lava that must have at one time poured from their sides. 

 I know that Prof. Dana, in a learned paper on the subject of 

 lunar volcanoes (Am. J. Sci. [2] ii. 375), argues that the 

 great breadth of the craters is no evidence of great ])rojectilc 

 force, the pits being regarded as boiling craters where force for 

 lofty projection could not accumulate. Although his hypo- 

 thesis is ingeniously sustained, still, until stronger proof is 

 urged, we are justified, I think, in assuming the contrary to 

 be true, for we must not measure the convulsive throes of 

 nature at all periods by what our limited experience has enabled 

 us to witness. 



"As regards the existence of volcanic action in the moon 

 without air or water, I have nothing at present to do, particu- 

 larly as those who have studied volcanic action concede that 

 neither of these agents is absolutely required to produce it; 

 moreover, the surface of the moon is the strongest evidence we 

 have in favour of its occurring under those circumstances." 



Doubtless volcanic action has been highly developed at the 

 surface of the moon, but in the absence of all water, we may 

 conclude that lava floods have rather been emitted from her vol- 

 canoes, than discharges of stones and ashes. 



It is still considered by some astronomers that the moon is 

 not altogether without an atmosphere ; though that be of small 

 extent, it may nevertheless be rich in oxygen. It M'ould be dif- 

 ficult to suppose that the extensive volcanic action which has evi- 

 dently taken place in the moon, could have been exerted or main- 

 tained without the presence of oxygen ; and if we admit that 

 aerolites come from that body, we must necessarily concede 

 there the existence of oxygen, since most aerolites contain a con- 

 siderable quantity of silica, magnesia and alumina. 



After all, the scarcity of oxygen where meteorites originate, a 

 fact in itself highly probable, as based on the non-oxidation of 

 the iron, nickel and phosphorus, if true, does not jn'ove they 

 proceed from the moon, but merely that they come from some 

 place deficient in oxygen. 



If meteoric masses of native iron really come from the moon, 

 their non-oxidation might arise more from the absence of aqueous 

 vapour than from an absence or deficiency of oxygen. While 

 fairly admitting that some aerolites have proceeded from lunar 

 volcanoes, because such have all the characters of erupted vol- 

 canic rocks, as those of Juvenas, Weston and Bishopville, it 

 by no means follows, as Dr. Smith would argue, that all meteoric 

 masses, even iron ones, also come from the same source or place; 

 for in many aerolites and meteoric irons there is little if any- 

 thing of a volcanic character. 



