1. Oceanic crust: This is denser and thinner than continental crust, typically made up of basalt and gabbro. It is found on the ocean floor.
2. Continental crust: This is less dense and thicker than oceanic crust, composed primarily of granite and other felsic rocks. It makes up the continents.
During subduction, the denser oceanic crust is forced beneath the less dense continental crust.