How does sedimentary rock change into igneous rock?
Sedimentary rock forms a relatively thin layer on the surface of the igneous rock. In some places, like the Canadian Shield there is no sedimentary rock and igneous rocks are at the surface. Other places, like near the Gulf of Mexico or the Hugoton Embayment of the panhandle area of the Great Plains, the sedimentary rock can be several miles thick. Igneous rock can be over 30 miles thick. It is thickest under the continents, and thinner under the ocean floor.
