Pg. 530, 575, 576, 577, 581. Caldwell Knob member. Top member of Seguin formation. Consists of a layer of oyster shells varying in thickness from a few inches to several feet, the average being about 1 foot. The oysters (in most places OSTREA MULTILIRATA) lie in matrix of calcareous silt, in most places cemented into hard sandy limestone. The bed has been traced by Julia Gardner from near Brazos River in Milam County to Rio Grande Valley and has been identified on Guerrero structure near Guerrero, Mexico. Is not continuous along outcrops.
Type locality: Caldwell Knob, 10 mi north of Bastrop and 2+/- mi south of Colorado River, Bastrop Co., east-central TX.

Source: US geologic names lexicon (USGS Bull. 896, p. 316).

Pg. 608-621. Redefined and reallocated to member status in Rockdale formation. As originally defined, Seguin formation straddles Midway-Wilcox boundary; a disconformity occurs within Solomon Creek member, which is here restricted to beds below the disconformity; Caldwell Knob is extended below to include all oyster and sand beds down to the unconformity. Where it is possible to recognize divisions as redefined, Caldwell Knob beds should be regarded as basal member of Rockdale formation. Where divisions cannot be differentiated, it may be necessary to continue use of Seguin formation, recognizing that it contains the break between the Midway and the Wilcox. Age is early Eocene (Wilcox).

Source: US geologic names lexicon (USGS Bull. 1200, p. 579).