Pg. 48 and passim. Monitor Mountain limestone member of Madison limestone. Top member of Madison limestone (lower Mississippian), nearly every good exposure of which in this area contains typical Madison fauna. Most striking feature of this member is its large amount of argillaceous matter. Lower 26 feet, fine-grained white argillaceous limestone, which breaks with conchoidal fracture and weathers light gray. Near base is 2.5 feet of gray fine-grained sandy quartzite. Overlying 54 feet is argillaceous fine-grained cream-colored limestone and some crumbly argillaceous limestone. Overlying this are 182 feet of white, slightly sandy argillaceous ragged limestones that weather clayey but of more white-gray color than underlying. Upper 20 feet, very massive thick-bedded pale buff-gray argillaceous limestone, which exhibits an occasional pinkish cast on fresh surfaces and weathers white buff. Thickness of formation 0 to 282 feet. Only known occurrence is in NE/4 sec. 18, T. 17 N., R. 7 W., on upper ridge and top of Monitor Mountain, [Caribou Peak 7.5-min quadrangle, Lewis and Clark County, northwestern Montana], where it is 282 feet thick. Overlies Rooney chert member. Age is Mississippian.

Source: US geologic names lexicon (USGS Bull. 896, p. 1398-1399).

Pl. 2 (column 38). Monitor limestone in Hannan limestone. Shown on correlation chart as the uppermost unit in Hannan limestone. Overlies Rooney chert. Age is Late Mississippian (Meramec).

Source: US geologic names lexicon (USGS Bull. 1200, p. 2554-2555).