Alright, John; You have made a very persuasive argument for shells not being re- absorbed in marine environments. So the question remains: where to dead shells go? The only thing I can think of is that they pile up on eachother year after year until the weight of them, the time, and the molecular replacement turns them into a new layer of limestone. Such limestone from Ordivician (and surrounding periods of time) here in Ohio and Kentucky are hundreds of feet thick. Then when the level of the limestone is raised by the action of plate tectonics, the limestone is weathered, goes down the rivers, and rejoins the oceans or makes new deltas. To watch this process experimentally probably takes more time than I have alloted---but I'm willing to try. Art