DeLong cyclical formation. [A name applied to a middle portion of Pottsville formation (Pennsylvanian) of central-western Illinois, based upon the rhythmic-cycle theory of sedimentation. Origin of name not stated.]

Source: US geologic names lexicon (USGS Bull. 896, p. 595).

Pg. 50 (fig. 22), 63, 73-76, 191, 192, 198, 199, 200, 201, 202, 203, 204, 205. DeLong cyclothems in Tradewater group. Occupies interval between Seville cyclothem below and Seahorne cyclothem above. Sequence includes three rudimentary cyclothems referred to as Lower, Middle, and Upper DeLong cyclothems. Consists principally of underclay, with soft shale and from one to four coaly streaks or thin coals; locally one or two thin sandstones are present but no limestone. Age is Pennsylvanian. Type exposure and derivation of name.
Type exposure: along Brush Creek in secs. 5 and 8, T. 9 N., R. 2 E., Galesburg quadrangle, Knox Co., IL. Named from town of DeLong which is about 2.5 mi northeast of type exposure.

Source: US geologic names lexicon (USGS Bull. 1200, p. 1083).

Pg. 42, 52 (table 2), pl. 1. DeLong cyclothem in Spoon formation (new) of Kewanee group (new). Name applied to cyclothem formerly called Upper DeLong. Above Brush cyclothem (new) and below Seahorne cyclothem. Age is Pennsylvanian. Presentation of new rock-stratigraphic classification of Pennsylvanian strata in Illinois; cyclical classification is independent of rock-stratigraphic classification.

Source: US geologic names lexicon (USGS Bull. 1200, p. 1083).