Numerical prefixes are used to denote lithologic discontinuities. The Cottonwood Limestone is noteworthy for the persistence of this lithologic character across its range. Under this criterion, crystals of kyanite appear upward of several meters from the lithologic change. The most desirable names are binomial, the first part being geographic and the other lithologic. The relationship to the term "Pottsville" and actual lithologic units is complex. Stratigraphy has two related subfields&colon; lithostratigraphy (lithologic stratigraphy) and biostratigraphy (biologic stratigraphy). These variations provide a lithostratigraphy or lithologic stratigraphy of the rock unit. First, the lithologic indicators of seasonality should span broad distances along the Pangean coasts.