By no process of external aggregation of solid matter to such a relatively small amount as that forming the moon, even if the aggregation was so violent as to produce heat enough to cause liquefaction, could any such long-continued volcanic action arise by gradual cooling, in the absence of internal gases.

There might be fissures, and even some outflows of molten rock; but without imprisoned gases, and especially without water and water-vapour producing explosive outbursts, could any such amount of scoriae and ashes be produced as were necessary for the building up of the vast volcanic cones, craters, and craterlets we see upon the moon's surface.
I am not aware that either Sir Robert Ball or Sir George Darwin have adduced this highly volcanic condition of the moon's surface as a phenomenon which can _only_ be explained by our satellite having been thrown off a very much larger body, whose gravitative force was sufficient to acquire and retain the enormous quantity of gases and of water which we possess, and which are _absolutely essential_ for that _special form of cone-building volcanic action_ which the moon exhibits in so pre-eminent a degree.

Yet it seems to me clear, that some such hypothetical origin for our satellite would have had to be assumed if Sir George Darwin had not deduced it by means of purely mathematical argument based upon astronomical facts.
Returning now to the problem of the moon's temperature, I think the phenomena this presents may be in part due to the mode of formation here described.

For, its entire surface being the result of long-continued gaseous explosions, all the volcanic products--scoriae, pumice, and ashes--would necessarily be highly porous throughout; and, never having been compacted by water-action, as on the earth, and there having been no winds to carry the finer dust so as to fill up their pores and fissures, the whole of the surface material to a very considerable depth must be loose and porous to a high degree.

This condition has been further increased owing to the small power of gravity and the extreme irregularity of the surface, consisting very largely of lofty cones and ridges very loosely piled up to enormous heights.
Now this condition of the substance of the moon's surface is such as would produce a high specific heat, so that it would absorb a large amount of heat in proportion to the rise of temperature produced, the heat being conducted downwards to a considerable depth.