quartzose sandstone, dark-gray, flaky-weathering shale, carbonaceous and/or sandy shale with local lignite, intensely cross-bedded, well-washed, fine- to coarse-grained sandstone, and variegated mudstone. The Dakota represents deltaic deposition along the margin of an eastwardly transgressing sea. Cross-bedded sandstone is interpreted as channel deposits; variegated mudstone represents flood-plain sediments. Carbonaceous or sandy shale and lignite are interpreted as lagoonal and marsh deposits near the seaward margin of the delta. Reed? molds may be observed in situ in siltstone with highly disturbed bedding beneath lignite beds at Stop 1. Gray shale at or near the top of the Dakota generally contains concretions or beds of clay-ironstone and locally contains arenaceous foraminifers suggestive of brackish water of interdistributary bays. Uppermost Dakota beds differ greatly in aspect in short distances and are commonly gradational with the Graneros, but evenly bedded sandstone that most commonly lies in this position is believed to represent shore-zone sand deposits that were redistributed during ultimate inundation of the deltaic margin by the advancing sea. Molds of marine mollusks are locally concentrated in great numbers in such beds at localities in Russell, Lincoln, and Mitchell counties. Localities in Russell and Lincoln counties contain a number of species that occur also in the Woodbine Formation of Texas (Hattin, 1965, p. 87), including Geltena obesa Stephenson, Brachidontes filisculptus var. microcostae Stephenson, and Anatimya longula Stephenson. Graneros Shale The nonuniform position of the Dakota-Graneros contact, as determined by reference to marker beds, reflects intertonguing of adjacent parts of the two units. Complexly varied lithology in the upper part of the Dakota gives way upward to more uniform lithology in the lower part of the Graneros Shale. In the immediate vicinity of the field-trip route, the Graneros Shale ranges from 24.9 to 36.4 feet in thickness, averaging 31.5 feet for nine complete sections in Russell, Ellsworth and Lincoln counties. The lower part of the formation consists mainly of dark-gray silty shale that is irregularly interlaminated with silt and fine sand and contains a few to several beds of thin-bedded, commonly cross-laminated, well- sorted, mostly noncalcareous quartzose sandstone. Distribution and abundance of sand, silt Figure 3.- Common macroinvertebrate fossils of Dakota, Graneros and Greenhorn Formations. (1) Geltena obesa Stephenson, upper part of Dakota Formation, X2; (2) Brachi- dontes filisculptus var. microcostae Stephenson, upper part of Dakota Forma- tion, X2; (3) Watinoceras reesidei Warren, Jetmore Chalk Member of Greenhorn, X2; (4) (9) Ostrea belolii Logan, upper part of Graneros Shale, 4 is X2, 9 is X1 1/3 (also occurs in lower part of Lincoln Limestone Member of Greenhorn); (5) Callistina lamarensis (Shumard), lower part of Graneros, X2 2/3; (6) Exo- gyra columbella Meek, lower part of Graneros, X2; (7) Inoceramus pictus Sowerby, Hartland Shale Member of Greenhorn, X1\frac{1}{2} (also occurs in Lincoln Limestone Member); (8) Plesiacanthoceras amphibolum (Morrow), upper part of Graneros, X1, (10) Inoceramus labiatus (Schlotheim), Jetmore Chalk Member of Greenhorn, X2/3 (also occurs in Pfeifer Shale Member of Greenhorn and lowermost part of Fairport Chalk Member of Carlile). 12