You ever look at these maps of continental drift and wonder if any other continents or islands existed that were subsided and are now lost?
Landmasses usually get plastered onto a continental edge when one plate dives beneath another, especially if the rock consists of lighter, less dense materials, as is the case with continents. Continental rock (typically "granitic" in composition [not necessarily granite, but of the same basic minerals as granite) is different than ocean floor rock. It is less dense and so 'floats' on the denser oceanic (basaltic) rock.
The Museum of Natural History here in New York has a hands-on exhibit where they have two rocks of the same size placed side-by-side, one is granite, the other basalt. There you can easily tell the difference in density between, the basalt being clearly heavier than the granite.