A substantial amount of chemical, isotopic, and textural evidence has accumulated indicating the activity of a deep sub-seafloor microbial biosphere on Earth. Microbial communities have been identified within hydrothermal vent systems at ocean floor spreading centers, deep within oceanic sediments, and at depth in the volcanic basement of oceanic crust. Questions remain as to how long such microbiological activity persists in the oceanic crust and how well it may be preserved in the geological record. Here we report chemical, isotopic and morphological evidence of relic microbial activity in the glass rims of 110 Ma pillow basalts at DSDP Hole 418A, North Atlantic Ocean (to a depth of 460 m into the volcanic basement). Petrographic studies of glassy pillow margins (using transmitted light microscopy) have revealed the presence of isolated networks of sub-microscopic anastomosing tunnels in the fresh glass. The tunnels occur at the glass/palagonite interface adjacent to fractures in the glass, and were not found to exist in olivine and plagioclase phenocrysts. FESEM imaging of basaltic glass chip samples has indicated that the tunnels are typically 150-200 nm across and are commonly in filled with material bearing resemblance to desiccated bacterial exopolysaccharides. Morphological and textural observations indicate that the tunnels may represent preserved nannoscopic trace fossils left behind by sub-micron sized organisms. X-ray mapping and point analyses (via electron microprobe) were carried out on basaltic glass samples displaying palagonite fabrics indicative of pre-existing tunnels. The mottled palagonite alteration fronts were found to contain high concentrations of C (up to 30 wt%) that correspond with significantly low values of CaO, MgO, and FeO, which is consistent with the presence of entrained organic carbon in the form of bacterial exopolysaccharides. Anomalously low delta carbon-13 values determined from disseminated carbonate (e.g., -13 per mil(PDB)) represent biologically fractionated carbon, and respective delta oxygen-18 values (e.g., 15-30 per mil(SMOW)) are consistent with a 15 to 110 degrees Celsius environment for the microbes.