Abrupt changes in lithologic character of the sediments as they pass from the subsidiary Delaware basin into the main Permian basin have made difficult the correlation of the Permian strata in the Pecos Valley. These sediments are here divided into three regional zones and an attempt is made to clarify by diagram their lateral relationships and to explain briefly the essential causes for their lithologic variations. A full section of Permian strata is shown and tentative correlations are proposed with formations of northern Texas and Oklahoma. The southern Permian basin presents the thickest and most continuous record of Permian sediments in the United States. Structural movement is suggested as the primary cause for reef development. The composition of a sediment commonl determines the color; the color of the Permian sediments is considered to be an index of the degree of salinity of the water in which they were deposited and to indicate their relative position in the basin at the time of deposition. The Permian sands are believed to have come from Llanoria and Appalachia.