Historical Account The earliest classification of Cretaceous strata in the Western Interior Region was by Hall and Meek (1856, p. 405) who subdivided the Missouri River section of Nebraska into units numbered 1 through 5, from the base upward. Geographic names based on places of typical exposure of these subdivisions were subsequently published by Meek and Hayden (1861, p. 419) in a comprehensive tabulation that included lithologic and paleontologic descriptions and thicknesses for each of the five formations. The names assigned were as follows: Formation No. 5 - Fox Hills Formation No. 4 - Pierre Formation No. 3 - Niobrara Formation No. 2 - Fort Benton Formation No. 1 - Dakota Cretaceous rocks were mapped in Kansas as early as 1857 (Hayden) but detailed study pro- ceeded slowly as evident in the remark by Swallow (1866, p. 10), in his first annual report as State Geologist of Kansas, that the "...Cretaceous is represented rather largely, but no definite examination has been made to show its extent, as it lies mostly beyond the settle- ments. Chalk is said to have been found in it." During the early 1870's, four expeditions led by O. C. Marsh and one by E. D. Cope entered the rich fossil field of western Kansas for the purpose of collecting vertebrate remains. From this work sprang a great volume of literature on fish, reptiles, and birds of the Niobrara Chalk, and a new generation of vertebrate paleontologists. In 1872, Hayden published one of the first detailed accounts of Cretaceous rocks in Kansas following a train trip on the Union Pacific railroad, which included the area be- tween Salina and Fort Wallace. Although Hayden recognized Formations No. 1, 2, and 3 in this work, Mudge (1875, p. 111) claimed that the Benton Group (No. 2) appeared to be absent in Kansas and stated further, "Hostile Indians and an uninviting country have kept explorers from traversing the southwestern plains." Shortly thereafter, Mudge (1878) not only recog- nized the presence of the Fort Benton but included in it the Fort Hays Limestone (now a mem- ber of the Niobrara Chalk). During this period Meek examined some Kansas baculitids that Mudge claimed were collected from the Niobrara. Meek suspected that the specimens came from Formation No. 4 or No. 5 (Pierre or Fox Hills)* but Mudge persisted in his belief that the baculitid beds in question were Niobrara. Ultimately, the beds containing the baculitids were referred to the Pierre Shale by Williston (1893). *These baculitids were collected at a locality near McAllaster, Kansas. Stop No. 6 of our trip is in the Pierre Shale at McAllaster. 2