Above is a picture of loosely-consolidated, fossiliferous mudstone from the Midway Group: a group of near-shore marine rocks exposed in southwestern Arkansas. The Midway Group was deposited in a variety of near-shore marine environments that were common in what is now Arkansas around 60 million years ago. The majority of the fossils pictured here are casts of a variety of sea snails (gastropods), but there are also oysters and tiny bryozoans (marine filter feeders).
To see more views of fossiliferous mudstone click here
Office of the State Geologist Blog 