Since the days of R. T. Hill (1901) two Upper Cretaceous lithic units have been used as formations but have remained unnamed. These two units have usually been called the "Lower Taylor Marl” and the “Upper Taylor Marl.” If Taylor is used as a group, both of these formations belong in the Taylor Group. If one uses Hill’s division system of classification, the "Upper Taylor Marl" belongs to the Taylor Division but the “Lower Taylor Marl" belongs to the Austin Division, since it is a claystone lithosome interfingering with the type Austin Chalk and is genetically part of the Austin.
Schuchert (1943, p. 900) may have been aware of some of the problems and some of the confusion rising out of this nomenclatural muddle when he applied the term “unnamed formation" to the unit generally termed "Lower Taylor Marl.”The "Lower Taylor" and the “Upper Taylor" are separated by the Pecan Gap Formation (Stephenson, 1918) so that the lithic sequence is claystone, chalk (or marly limestone), and claystone. In more detailed maps of the greater area of Austin, Texas, the Pecan Gap is omitted by faulting in some areas, leaving the two claystone formations in fault contact. To eliminate confusion, it is imperative that the two unnamed claystone units be named.