Geologic Unit: Crystal Falls

Usage:

Crystal Falls Limestone [unranked] in Harpersville Formation of Cisco Group (TX-notably south of Brazos River)
Crystal Falls Limestone [unranked] in Markley Formation of Bowie Group (TX-notably north of Brazos River)
Crystal Falls Limestone Member of Thrifty Formation of Cisco Group (TX*)

Geologic age:

Late Pennsylvanian (Virgilian)*

Type section, locality, area and/or origin of name:

Named from town of Crystal Falls, Stephens Co., Brazos River region, central northern TX (Plummer and Moore, 1922).
Type section in Stephens Co., central northern TX: measured from shale beneath Breckenridge limestone to top of "Upper Crystal Falls" limestone. Beds 1-4 of section (fig. 6 and pl. 2, A) crop out on State land and beds 4-14 on property of Truman Robertson of Crystal Falls. Breckenridge limestone crops out in bed of Clear Fork of Brazos River from dam beneath bridge on Farm Road 578, down stream to first bend. Lower part of section (fig. 6, beds 1-7C) was measured southwestward from first bed below dam (pl. 2, A), across the dam and old bridge road to good exposure of railroad cut no. 1; upper part of Quinn clay (bed 5) is well exposed at clay exposure no. 1. The interval from the top of Crysal Falls limestone to coal in Curry clay was described at clay exposure no. 2 (beds 7C-11), about 25 yds southwest of railroad cut no. 1; the offset is along bed 7C. Upper part of section (beds 11-14D) was described in railroad cut no. 2 to west; offset correlated with coal (bed 11) (Brown, 1960).

AAPG geologic province:

Bend arch*