Thanks for the Sansa Clip suggestion. It looks like I'll definitely have to buy a compatible device to listen to audible books because audible will not play on just any MP3 player. They're as protectionist and anti-competitive as Australian publishers.
No rock is completely impermeable, but some porous rocks like shale and pumice are mostly impermeable, because the pores are not interconnected, thus not allowing fluids or gases to pass through them. This is why shale makes a good cap-rock, and pumice floats instead of sinking.
Selective Permeability The cell membrane has selective permeability. This means that it allows some materials, but not all, to cross it, or permeate it. In other words, the cell membrane is semipermeable. You might own a semipermeable jacket. The jacket is waterproof; it does not allow water in from the outside. But water vapor from your sweat can