Stratus (St) Found at very low levels (less than 2000 meters, or 6500 feet), stratus clouds are thick, large, heavy-looking gray clouds that dominate the sky. Precipitation normally does not occur with this cloud, although drizzle or mist may be observed.
Shale is a fine-grained sedimentary rock which is formed by the compaction of silt and clay-size mineral particles. Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism.
Slate is a metamorphic rock. Metamorphic rocks are rocks that change form from one type of rock into another because of time, pressure, heat and other factors. Other metamorphic rocks include slate, shale, schist, gneiss and marble. The new form of a rock is determined by the composition of the original rock. Shale doesn't automatically turn into slate.