The Haymond Formation of the Marathon basin, Texas consists mainly of a sequence of more than 12,000 siltstone-shale couplets which, combined with the similar couplets of the older Tesnus Formation, form a sequence of flysch sediments more than 10,000 feet thick deposited on the eastern slope of the subsiding Llanoria geosyncline. The Haymond Formation contains no diagnostic fossils; its age is known only as Lower Pennsylvanian, probably Atokan
