Includes bibliographical references (pages 36-38) and index.

Introduction -- Geology -- Methods of Analysis / A note on Conifer Taxonomy -- ABO Formation / Age and Depositional Environment ; Fossil Flora -- Base of Red Magdalena / Fossil Flora ; Age of Environmental Implications of the Flora -- Unit 8 / Fossil Flora ; Stratigraphic and Environmental Interpretations -- Unit 10 / Fossil Flora ; Stratigraphic and Environmental Interpretations -- Unit 35 / Fossil Flora ; Stratigraphic and Environmental Interpretations -- Discussion

Plant fossils are described from five stratigraphic levels in upper Paleozoic strata in Abo Canyon, New Mexico. The fossils were collected by Charles B. Read, of the U.S. Geological Survey, in 1940 and 1941, and span the Pennsylvanian-Permian boundary. Read's original field notes have not been located. However, a combination of his pattern of bed numbering, notes written by Read and enclosed with the collections, and the taxonomic composition of the floras permit them to be placed with confidence in a sequence from oldest to youngest. The youngest fossils, which securely anchor the entire collection stratigraphically, are from the Abo Formation and are of early Permian age. A collection labeled "Base of Red Magdalena" is most likely from what today would be termed the Bursum Formation, thus immediately below the Abo. The three remaining collections are from the Pennsylvanian-aged Atrasado Formation, probably the Upper Pennsylvanian portion, extending as far back as the Missourian. The collections record a trend of increased seasonality of moisture (likely rainfall) through time. They are all either dominated or co-dominated by plants typical of environments with seasonal moisture stress. Conifers, Sphenopteris germanica and mixoneurid odontopterids are common to abundant in the collections older than the Abo Formation. All of the assemblages from below the Abo Formation also contain some taxa that required wet substrates for most of the year, particularly calamitaleans and marattialean tree ferns; the oldest collection also contains evidence of arborescent lycopsids.- -