Which type of rock is formed from ancient clay beds?

The correct answer is shales. Shale is a type of sedimentary rock that forms from the compaction of clay particles over long periods, typically in ancient environments such as lake beds or ocean floors where fine particles can settle. This rock is characterized by its layered structure and ability to easily split along those layers due to its fine-grained composition.

Shales often contain organic material and can serve as important reservoirs for hydrocarbons. Understanding the formation of shales helps in various geological and drilling practices, as they can also indicate the presence of certain resources and inform drilling strategies.

Other types of rocks listed, such as granites, limestones, and sandstones, have entirely different formation processes. Granites are igneous rocks formed from the slow crystallization of magma beneath the Earth's surface. Limestones are sedimentary rocks primarily made from calcium carbonate and often originate in marine environments from the accumulation of shell debris or calcium-rich sediments. Sandstones, also sedimentary, are composed of sand-sized particles and are typically formed from the consolidation of sand deposits. Each of these rock types presents distinct characteristics and formation histories, which are crucial to understanding geology and subsurface conditions.