Here's why:

* Continental crust is thicker and less dense than oceanic crust. It's made up of mostly granite and other felsic rocks.

* Oceanic crust is thinner and denser, composed mainly of basalt and gabbro.

The continental margin represents the transition zone between the continent and the ocean. While the continental shelf and slope are part of the continental crust, the continental rise is formed by sediment deposition and may include some oceanic crust fragments.

However, the majority of the continental margin is made up of the continental crust that extends outward from the continent itself.