The stratigraphic relations of the formations of the Trinity group (Lower Cretaceous), at the outcrops in southwestern Arkansas, southeastern Oklahoma, and northern Texas are described briefly and represented graphically by cross sections and a correlation diagram. A new unit in the Arkansas section, the Holly Creek, is defined. Another unit, the Paluxy, is recognized and shown to be continuous across southeastern Oklahoma into the typical Paluxy of northern Texas. The Dierks-DeQueen interval of Arkansas-Oklahoma is correlated, first with the Glen Rose of northern Texas, then with the upper Glen Rose of northwestern Louisiana, on the basis of stratigraphic position and fossils. Two units of the Trinity group in the northwestern Louisiana section, not heretofore described, are briefly mentioned. The one is a thick series of red beds underlying the Glen Rose. The other is a still older series of shales and limestones with Lower Cretaceous fossils. Several new characteristic micro-fossils are noted from zones in the Trinity.