The Marshall Ridge limestone showing is on the north side of Carpenter Lake on a precipitous slope, 3.5 kilometres south of Marshall Lake. The limestone is within a sequence of chert, argillite and chloritic schist of the Mississippian to Jurassic Bridge River Complex (Group), and is exposed over an area of 900 by 500 metres. A sample of limestone contained 96.73 per cent CaCO3, 1.83 per cent MgCO3, 0.46 per cent SiO2, 0.23 per cent Al2O3 and 0.17 per cent Fe2O3 (Geological Survey of Canada Summary Report 1916, page 53).