Circular 39 — Preliminary Observations on the Mississippian System of Northern New Mexico

By Augustus K. Armstrong, 1955, 42 pages.

Study of fossil collections from the lower limestone member of the Sandia formation in northern New Mexico, which hitherto has been regarded as Pennsylvanian, shows that this part of the section is actually Mississippian. In the Sangre de Cristo Mountains, the Meramec only may be represented, but in the San Pedro, Nacimiento, Jemez, and Sandia Mountains, the lower barren portions of the limestone section may be of an earlier Mississippian age.