The Monument Creek group
Introduction PREVIOUS WORK The Monument Creek group is the name introduced by Hayden, 2 in 1869, for the “series of variegated beds of sands and arenaceous clays . . . of various colors . . . and of various degrees of texture” which occur on the Platte-Arkansas Divide along the base of the Front Range in Colorado. Since their first description these rocks have been often referred to, notably by Hayden, 3 Cope, 4 Emmons, 5 Eldridge, 6 Lee, 7 and Darton. 8 Hayden at first considered the Monument Creek group “Modern Tertiary,” on the basis of its general appearance and uncon-formable relations to the underlying Cretaceous strata, but because of the fossil plants found in the group he suggested its equivalence to a portion of the “Lignitic” group. Later, influenced by Cope, Hayden was “inclined to regard it [the Monument Creek group] as Miocene.” In 1874, on the basis of vertebrate fossils, Cope concluded that the . . .