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.
The major difference between shale and sandstone is the type of materials from which they are formed and the size of the particles. Shale is made primarily from clay and has a much finer grain that sandstone. Sandstone is made primarily of sand and has a larger grain.