> --- Joerg Baumgartner <joe_at_...> wrote:
> Would any of these allow for underground rivers, and a > tunnel system? My guess would be limestone?
Limestone is probably the most soluble of these minerals, but you'd be astonished what happens to quartz in the presence of water under pressure (say a huuuuuuuge stomping foot).
The best recipe for caverns are limestone (or marble) inclusions in rock harder to dissolve, and then some source for chemically active water (volcanic springs, gorp, krarshtkids, huge amounts of burning).
My personal favourite for the rock still is quartzite. My original suggestion that riverine quartzite was brought here all the way wasn't taken over by the Barbarian Adventures description (inherited by DP:LoT), so now we have a whitewalled fort on a white-walled cliffside (which, at least to my inner eye, cheapens the effect).
A pegmatite with a whitish feldspar plateau above a hydrothermal quartzite enclosure which was made to blossom up through the cracks by a mythological force (hot water sent by Vestkarthen, shock by Larnste folding up the Storm Mountains, a foe of Destor falling to the ground), providing large irregular bricks of snow white quartzite would appeal to an artist to use it for fortress building. The Feldspar plateau would have fairly slick walls, somewhat stable vertically. The surface would provide better farming than the Aran Isles, though not significantly so - best use would be to carry up grass sods and use this for grazing, with a few sheltered gardening plots for plant food.
Sapping through either limestone or feldspar up a plateau seems pretty hopeless if done by conventional means. If I were the Lunar commander in charge of the siege, I'd hire krarshtkids for that job. The question is how good Uroxi Sense Chaos works through the bedrock.
Access tunnels lead to bridgehead positions. These might be useful. Access to the tunnel system below would even be a nastier scenario - tunnel fighting tends to be dirty. Neither force has ready specialists for that, either side could hire some - trolls, Mostali, Scorpion Folk, Krarshtkids, Elementals.
Sapping to collapse the defensive position is harder on the plateau premise. You could try to collapse the side of the plateau. Limestone would be the easier material for that, just visit the cliffs of Dover.
I take it as a given that there are troll and krarshtkid tunnels in the area, upsetting most plans for underground rivers. I know of four major underworld leaks in the region, too (Tarpit, Blackwell, Zatarn Lake, Print).
Chemist speaking alert:
If the Heler rains really turned acid, the vegetation would have died, but otherwise have been just fine. Limestone, however, would react to (really) acid rain like snow fortifications around freezing to cold water. The resulting mess would probably be a light grey sludge.
If it is raining a fermentation agent, then the rocks would survive but vegetation be washed away. Mythically feasible, but pretty please don't just call it acid.
If it is raining Gorp sludge, similar effect, but then why are we talking about "Heler's" rain?
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