Shale is a sedimentary rock, formed by the deposition and compression of clay and silt.
Shale layers is buried deep into the earth through the process of deposition (i.e the laying down of rock forming material by natural entities like glaciers, wind, and water).
Temperatures and pressures rise greatly because the shale’s layers are buried. When the temperatures and pressures become higher. The shale is changed into a metamorphic rock (with dark brown streak), called Slate.
