ABSTRACT
All of the Paleozoic rocks of the Marathon Mountains have been referred to as having been deposited in the Llanoria geosyncline. The Pennsylvanian rocks of the Marathon Mountains are the thickest of any Pennsylvanian rocks known in West Texas but the pre-Pennsylvanian rocks, with the possible exception of the Cambrian sandstone, attain their maximum thicknesses north and west of the Llanoria geosyncline.
The Llanoria geosyncline, if it is considered as a deep trough developed adajcent to the old landmass of Llanoria, was not developed until the end of Mississippian time. Only Pennsylvanian rocks can be considered as having been deposited in the Llanoria geosyncline.
Diagrammatic cross sections show the different positions of the axis of maximum deposition in West Texas from Ordovician time through the Pennsylvanian period.
