This is laminated siltstone showing small scale slump structures of a type generally called convolutions, or (in more extreme cases) 'ball and pillow' structure. Such structures occur on a range of scales, and are quite common. I have seen them in Spain, Ireland and several parts of the UK.
Your specimen may also have been slightly deformed tectonically (the bend in the middle).
Stromatolites can have a somewhat similar apperance, but you'd need to be in an appropriate geological terrain.