Answer the following question given this paragraph: 

A geologic map shows the different rocks that are exposed at the surface of a region. Rock units are shown in a color identified in a key. On the geologic map of the Grand Canyon, for example, different rock types are shown in different colors. Some people call the Grand Canyon “layer cake geology“ because most of the rock units are in layers. Rock units show up on both sides of a stream valley.


Q: What are the three main types of rocks?


A:
sedimentary, igneous and metamorphic