First: your map decides the materials. Whether a material exists — and whether you can dump it back onto the ground — is decided by your map and mod list, not by this mod. The base game only knows STONE; DIRT, GRAVEL, SAND, COAL, LIMESTONE and PAYDIRT always come from maps or mods. And the game caps ground materials at 63, 48 of which the base game uses itself — on big mod lists the last slots go fast. Mining Layers takes a middle road so it stays playable on every map: it checks on load what your map really provides and only offers that. A (!) in the layer picker means: digging and selling work, dumping doesn't on this map. If something is missing, it's the map — not the mod.