<P> Like the Supai Group below it, the Permian - aged Hermit Formation was probably deposited on a broad coastal plain (see 6a in figure 1). The alternating thin - bedded iron oxide, mud and silt were deposited via freshwater streams in a semiarid environment around 280 million years ago . Fossils of winged insects, cone - bearing plants, and ferns are found in this formation as well as tracks of vertebrate animals . It is a soft, deep red shale and mudstone slope - former that is approximately 100 to 900 feet (30 to 274 m) thick . Slope development will periodically undermine the formations above and car - to house - sized blocks of that rock will cascade down onto the Tonto Platform . An unconformity marks the top of this formation . </P> <P> Coconino Sandstone formed about 275 million years ago as the area dried out and sand dunes made of quartz sand invaded a growing desert (see 6b in figure 1). Some Coconino fills deep mudcracks in the underlying Hermit Shale and the desert that created the Coconino lasted for 5 to 10 million years . Today, the Coconino is a 57 to 600 feet (17 to 183 m) thick golden white to cream - colored cliff - former near the canyon's rim . Cross bedding patterns of the frosted, fine - grained, well - sorted and rounded quartz grains seen in its cliffs is compatible with an eolian environment . Also fossilized are tracks from lizard - like creatures and what look like tracks from millipedes and scorpions . An unconformity marks the top of this formation . </P> <P> Next in the geologic column is the 200 - foot (60 m) - thick Toroweap Formation (see 6c in figure 1). It consists of red and yellow sandstone and shaly gray limestone interbedded with gypsum . The formation was deposited in a warm, shallow sea as the shoreline transgressed (invaded) and regressed (retreated) over the land . The average age of the rock is about 273 million years . In modern times it is a ledge - and slope - former that contains fossils of brachiopods, corals, and mollusks along with other animals and various terrestrial plants . The Toroweap is divided into the following three members: Seligman is a slope - forming yellowish to reddish sandstone and siltstone . Brady Canyon is a cliff - forming gray limestone with some chert . Wood Ranch is a slope - forming pale red and gray siltstone and dolomitic sandstone . An unconformity marks the top of this formation . </P> <P> One of the highest, and therefore youngest, formations seen in the Grand Canyon area is the Kaibab Limestone (see 6d in figure 1). It erodes into ledgy cliffs that are 300 to 400 feet (90 to 100 m) thick and was laid down in latest early Permian time, about 270 million years ago, by an advancing warm, shallow sea . The formation is typically made of sandy limestone sitting on top of a layer of sandstone . This is the cream to grayish - white rock that park visitors stand on while viewing the canyon from both rims . It is also the surface rock covering much of the Kaibab Plateau just north of the canyon and the Coconino Plateau immediately south . Shark teeth have been found in this formation as well as abundant fossils of marine invertebrates such as brachiopods, corals, mollusks, sea lilies, and worms . An unconformity marks the top of this formation . </P>

What geological forces were responsible for the formation of this folded gneiss from arizona