I. Introduction. In describing the clays which underie the Chalk at Speeton on the Yorkshire coast in a paper communicated to this Society in 1889, I attempted to show the necessity for a fresh classification of these deposits.Further investigation of this section has fully confirmed the views then advanced. It has also indicated the desirability of a corresponding revision of the inland exposures of the rocks of the same age in Yorkshire and Lincolnshire, since it is only by means of the knowledge of the full sequence to be acquired on the coast-section that the true relationship of the limited and isolated exposures of the interior can be unravelled. Using such opportunities as have at intervals occurred, I have therefore more or less closely examined the base of the Chalk escarpment throughout its whole length in Yorkshire and Lincoln-shire, and desire in this paper to put on record the result of my investigation. It will be shown that the divisions proposed for the Speeton section are readily applicable to the inland exposures, and indeed afford the most convenient and natural means of palæ-ontological classification, albeit some modification of the systems, usually applied is thereby required. It may be well at once to state that, while my chief aim will be to establish the correlation of the deposits by means of their palæontology, no attempt will, for the present, be made to carry the palæontological research further than is necessary for this purpose. Hence the fossils dealt with herein will only