After many years of study of the graptolite zones of the slate belt of eastern New York, Ruedemann became convinced that the bedded cherts represent more than a mere phase of the shale, and that the problem of their origin is one for detailed study, together with the question of the depth of deposition. Accordingly, their relative abundance, their stratigraphic position, their petrographic structure, and their paleontologic content have been the subject of special investigation. These studies disclose a radiolarian fauna in the chert, that suggests, for the chert and the accompanying graptolite shales, a syngenetic colloidal origin and deposition in the deeper reaches of the geosyncline.