sentence meaning involving negation

Question

"But this small gravitative power of the moon would prevent its retaining on its surface any of the gases forming our atmosphere, which would all escape from it and probably be recaptured by the earth. 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." From Is Mars Habitable? by ALFRED RUSSEL WALLACE F.R.S., ETC.

I am not a science expert at all, so I don't think myself fully understand the content of the excerpt above. But I cannot bring myself out of doubt that the highlighted part is positive sentence, considering the preceding sentence which is in negation. So the cluase in the highlighted part should be also negative, I guess. What I mean is not based on syntax, but semantics. What I undertand as follows: Volcanic activity cannot occur without internal gases(imprisoned gases), and no matter how powerful external aggregation is, it cannot make volcanoes on the moon. Please help me.

Answer 1

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 interpret this as a rhetorical question, to which the implied answer is "no" or "probably not". (I would therefore add a question mark.)

"As were necessary" here is an archaic way of saying "as would be necessary".

The essay was written well over a century ago, in 1907, by a man who was born in 1823. So we should not be surprised that it is not phrased in a particularly modern way.

Answer 2

Think of something with a soft cushion, like a pillow or bed. The softness comes from air inside that gets compressed. Tables and beds are pretty similar -- the biggest difference is the soft mattress on the bed. Put something heavy on a weak table and the table will just crack (like a fissure) and break. But put something heavy on a bed, and the mattress will "crater" before the frame breaks.

Also, think about toilet paper: the cheap stuff you might find in a public toilet versus the quilted 2-ply or 3-ply you might buy yourself. The quilted TP is "squeezably soft" because of all the air trapped inside, but the cheap TP is usually pretty hard because of how much paper the manufacturer tries to include.

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.

The author is stating that although there is evidence of volcanic activity, there's not the right kind of volcanic activity. Without the explosive force of trapped gases, and an atmosphere for dust and ash to both mix with and be moved by, the ground of Mars will not be conducive to the creation of Moon-like terrain.