13.1 Why are continents high and oceans low?
Fig 13.4
Demonstrating isostasy
The base of a floating wood block must be at the same pressure as the water at that point in the water.
Here we see wood blocks of varying density. Isostasy clearly shows that lower density materials should project higher. Higher density blocks sit lower in the water than low-density ones.
The proportion of a block projecting is always the same for a given density.