ART. VI.--Mississippian (Lower Carboniferous) Formations in the Rio Grande Valley, New Mexico;: Introduction. Lake Valley Limestone. (Mississippian.) Percha Shale. (Devonian.) Mimbres Limestone. (Siluro-Ordovician.) Fossils from Lake Valley. Fossils from Hillsboro. Fossils from Kingston. Fossils from Cooks Range.