conditions for growth of the species during deposition of that part of the Jetmore. Numerous lenses of hard skeletal limestone in these upper beds indicate occasional stirring of bottom sediments by currents or waves. During this time interval, generally better circulation and perhaps also a slower rate of sedimentation aided the establishment of a limited epi- fauna including Ostrea, rare cirripeds and very rare Discinisca. Of course, the barnacles may have been attached to floating debris, but Ostrea is attached to valves of I. labiatus. Other known fossils in the Jetmore are cephalopods including Watinoceras reesidei (common), Baculites cf. B. besairiei (sparse), Mammites (rare), and Tragodesmoceras bassi (sparse). Pfeifer Shale Member.- The Pfeifer consists chiefly of laminated chalk and chalky lime- stone but differs from the Jetmore in having numerous irregular beds and concretions of chalky limestone as well as more or less even layers of such rocks. The layers of limestone are believed to be essentially time parallel because of uniform position with respect to ben- tonite marker beds. This member is approximately 21 feet thick in the field-trip area. Depositional conditions that prevailed during the latter half of Jetmore time continued little changed during accumulation of the Pfeifer. Shaly chalk in the lower two-thirds of the member contains a profusion of Inoceramus valves. Abundance of shell debris in chalky limestones in this part of the Pfeifer suggests that such beds may have originated during wave or current stirring of carbonate mud on the sea floor. Concretions of chalky limestone contain fewer fossils than the other limestone beds and formed by cementation of carbonate mud around one or more shells that usually were whole, or around other fossils. Early diagenetic origin is demonstrated by preservation "in the round" of contained fossils and bending of adjacent chalk layers around the concretions as a result of compaction. Inoceramus labiatus dominates the Pfeifer macroinvertebrate assemblage and Inoceramus cuvieri Sowerby makes its first appearance in the upper part of the member. Ostrea is a common epizoan on Inoceramus shells, and barnacles are attached sparingly to valves of I. cuvieri. Other Pfeifer fossils include Collignoniceras woollgari (Mantell) which is found in the upper few feet of the member, Teredo-like borings in petrified wood, Watinoceras (sparse), juvenile hamitid? cephalopods, and a smooth species of Baculites. In addition, Morrow (1941) has reported Mammites in the Pfeifer Member. Carlile Shale Fairport Chalk Member.- Although the Fairport Chalk Member has been classified historically as a member of the Carlile, the unit is genetically related, both faunally and lithologically, to the Greenhorn Limestone. Furthermore, the lowermost part of the Fairport is indistinguishable from the Pfeifer Shale Member of the Greenhorn, suggesting need for upward shift of the exist- ing Pfeifer-Fairport boundary. Additionally, the Fairport fulfills all qualifications for 16