Character.—Blue to bluish gray, thin-bedded, fine-grained limestones and shales, with some oolitic, concretionary, and intraformational conglomerate layers.
Thickness.—In Blacksmith Fork, 759 feet; in the section west of Liberty, 731 feet.
Organic Remains.—Abundant Middle Cambrian fossils.
Spence Shale
Type Locality.—Spence Gulch, a ravine running up into Danish Flat from Mill Canyon, about 5 miles west-southwest of Liberty, Bear Lake County, Idaho. This shale occurs at the base of the Ute formation.
Derivation.—From Spence Gulch, the type locality.
Character.—Argillaceous shales.
Thickness.—In the section west of Liberty, 30 feet; in Blacksmith Fork, 30 feet.
Organic Remains.—An extremely abundant and varied lower Middle Cambrian fauna.
Langston Formation
Type Locality.—The most readily accessible locality for this formation is in Blacksmith Fork, but the strike of the beds (as shown on the eastern half of Map 3 of the Fortieth Parallel Survey) carries the formation into the valley of Langston Creek, and the formation is given that name.
Derivation.—From Langston Creek.
Character.—Massive bedded, bluish gray limestone with many round concretions.
Thickness.—In Blacksmith Fork, 107 feet; in the section west of Liberty, 30 feet.
Organic Remains.—Lower Middle Cambrian fauna.
Brigham Formation
Type Locality.—West front of the Wasatch Range, northeast of Brigham, Box Elder County, Utah.
Derivation.—From Brigham, near the type locality.
Character.—Massive quartzitic sandstones.
Thickness.—At Brigham, 2,000+ feet; in Blacksmith Fork, 1,250 feet; and in the section west of Liberty, Idaho, 1,000+ feet.
The Brigham formation is the overlapping shore deposit of Middle Cambrian time along what is now the Wasatch Range. To the northwest, in the Belt Mountain region of Montana, the upper part
