In the course of field work in North-East Yorkshire on the Dogger and associated rocks, in which we have now been engaged for some years, we have found several occurrences of a rock which we may call Black Oolite. In order to prevent any misunderstanding it will be well to say at once that this is not the magnetite-oolite of Rosedale, so often mentioned in the literature and no longer exposed, but quite a different type, which does not appear to have been described by any writer, though well worthy of special investigation. This is the more remarkable in that all the sections known to us where it occurs are referred to in nearly all the standard works. Incidentally we should like to remark that over and over again we have been amazed at the inadequacy and often the entire incorrectness of the petrographical descriptions given in the literature of numerous admirable exposures throughout the district. Not seldom we have found it impossible to reconcile with these descriptions our measurements and petrographical determinations of such sections, although there can be no doubt of their identity; it should also be remarked that sixty or seventy years ago many of these sections, especially in alum works, must have yielded even fresher and more easily determinable material than they do to-day.