Publisher's Synopsis
Conician rocks are widely distributed in the western interior of the United States. Reeside noted that these rocks occurred in three north-south belts: an eastern belt of chalk and lime mud, a middle belt of dominantly calcareous to non-calcareous shale, and a western belt of mostly sandstone. Limestone concretions in the middle shale belt contain the bulk of the Coniacian ammonites known from the region, and these have been investigated by Meek and Hayden (1862), Meek (1864, 1876), Stanton (1894), Reeside (1927a, 1927b, 1932) and Cobban (1951a, 1952a, 1952b, 1961).;Since the publication of the last systematic work in 1961, many new collections of Coniacian ammonites have been made, and these together with earlier collections of undescribed material form the basis of the present investigation.
