Blacklead limestone. Massive, thick-bedded limestone greatly resembling the grayish thick-bedded Paleozoic limestones in Montana, and in Idaho southeast of Salmon River Mountains. Considerably metamorphosed by intrusives, so that no fossils are preserved, but bedding is everywhere distinct. Magnetite in seams and lenses is extensively developed through the limestone along bedding planes and fractures, the result of contact metamorphism. Thickness 400+ feet; base not exposed. Lies far back in Clearwater Mountains, at head of Cayuse Creek, a tributary of North Fork of Clearwater River. Forms an engulfed block or pendant 2+/- miles long and 0.5 mile wide near north margin of Idaho batholith, in a high glaciated valley between Blacklead Peak and Rhodes Creek. Assigned to Paleozoic(?) (pre-Permian).
[Derivation of name not stated, but almost certainly is Blacklead mining district, Orofino region, Clearwater Co., northern ID.]

Source: US geologic names lexicon (USGS Bull. 896, p. 203).

Pg. 701, chart (column 49b). Blacklead limestone. No proof of the existence of deposits representing Morrowan, Lampasan, Missourian, or Virgilian time is known in the Wood River or Blacklead limestones; [J.S.] Williams believes that Missourian and perhaps Virgilian deposits are represented.
[Misprint: US geologic names lexicon (USGS Bull. 1200, p. 367) states "Age shown on chart as Mississippian and Pennsylvanian." Should be "Age shown on chart as Pennsylvanian."]

Source: Publication; GNC index card files (USGS-Menlo); US geologic names lexicon (USGS Bull. 1200, p. 367).