You're sinking a mine shaft, not stacking a tower. Ore chunks fall from the top — rotate and slide them to complete a row across the shaft. Every completed row is a metre dug, and the rock here is rigid: a cleared row empties in place and the wall above never settles down into it, so whatever shape you leave behind is the shape you have to work with. Fresh rock keeps pushing up from below, and if it shoves you out of the top of the shaft the run ends.
Granite, water pockets and hardpan are in the rock from the first chunk, and they thicken the deeper you get. Granite cracks for free in the same cascade. A burst water pocket pours down and pools in whatever space you left open, then seeps away slowly. Hardpan has to be completed twice — the first pass only cracks it — which is what closes the shaft on you near the end. Break through at 100m and you win. Deep Dig is an original game made for GameMyself, with a hold slot, a ghost landing marker, and a best depth saved only on this device. No download, no account.