A petrographic study of the Meagher Formation of Cambrian age indicates that it was deposited on a stable shelf. Deposition occurred in marine banks and shoals. Textural and structural features of the carbonates include oolites, micrites, microsparites, crossbedding, and mottling. Control of mottling is classified as depositional, organic, and diagenetic. Recrystallization of micrite to microsparite is recognized. Dolomitization was widespread in southwestern Montana and selective in other parts of Montana where the Meagher was studied.