They are too shallow for ships
Physical map, topographic map, climate map, economic or research map, road map, and thematic map
That is because metamorphic rock is formed by parent rocks that are either sedimentary rock or igneous rocks and we can use the former rock type to distinguish the type of metamorphic rock, marble was igneous rock exposed to high pressure or temperature.
While the other two type of rocks are formed initially by sedimentation and volcanic movements and has no parent rocks.
