Scanning electron microscope examination of quartz grains obtained from lacustrine limestones marginal to an alluvial fan in the middle Carboniferous Parrsboro Formation (Riversdale Group) reveals surface characteristics typical of glacial transport. This suggests that a paleoclimate sufficiently cool to support mountain glaciation may have existed in the northeastern Appalachians during middle Carboniferous time. This evidence of a cool paleoclimate is contrary to conventional interpretations of Carboniferous paleoclimates, which are considered to have been warm. The glacially modified quartz grains may represent a paleoclimatic event that can be used in stratigraphic subdivision of middle Carboniferous strata and can also be used to separate the Canso and Riversdale Groups of the middle Carboniferous of eastern Canada. The boundary between the Canso and Riversdale Groups is, at present, recognized as being of a time-transgressive nature.