 The record of this long history can be read in the many rock layers deposited over time through the forces of erosion, volcanic activity and plate subduction.These different forces have made a geologic mosaic made up of volcanic island arcs, deep ocean sediments, basaltic ocean floor, parts of old continents, submarine fans, and even pieces of the deep subcrustal mantle of the earth.The disparate pieces of the North Cascade mosaic were born far from one another but subsequently drifted together, carried along by the tectonic plates that make up the Earth's outer shell or were uplifted, eroded by streams, and then locally buried in their own eroded debris; other pieces were forced deep into the Earth to be heated and squeezed, almost beyond recognition, and then raised again to view.