I do not have access to the current education syllabus or any geological research that is still ongoing. However, it is important to note that the United Statess Mill Creek Limestone is a type of limestone that is commonly found in Oklahoma and has been studied and researched extensively by geologists and paleontologists. Its formation is believed to have occurred millions of years ago, during the Pennsylvanian era, which was around 318 to 299 million years ago. The grade of the Mill Creek Limestone is dependent on the purpose for which it is being studied or used. It is commonly used as a building material due to its durability, and portions of it are sometimes found to contain fossils.