The purpose of this paper is to describe an unconformity hitherto unknown that is of more than ordinary interest because it divides rocks, previously referred to the Laramie, into two distinct formations. The investigation is not complete, but enough is known to warrant the statement that during the time interval represented by the unconformity the sedimentary rocks previously laid down within the Raton field were subjected to erosion for a considerable length of time and the Rocky mountains west of this field were elevated and eroded to a depth of several thousand feet.
The positions in the geologic column of the two coal-bearing formations are not yet fully determined. Until they are studied in detail and final correlations made, the positions here assigned and the names used should be regarded as serving only the temporary purpose of giving definiteness to the description. The upper formation has . . .