[math-fun] conical fallacy

Where is the misapplication of integral calculus in the following?: While preserving its edge, deform the base of a circular, say, cone to make it convex or concave, with area A. Then the volume formula should remain V = A h/3, because you can decompose it into a tapered series of curved plates dV = A (z/h)^2 dz. And I am the Virgin Mary. --rwg