Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/490

 Grimston. Between this last point and Sancton, the red-rock overlaps successively the different members of the Lias, and at the last- mentioned place, the representative of the Inferior Oolite, now reduced to a very thin bed, is again uncovered. As we approach the Humber, the Kelloway, the Oxford, and the Kimmeridge successively reappear from beneath the Chalk ; and crossing into Lincolnshire we recover the Lower (?) Neocomian at Worlaby, the Middle Neocomian at Clixby, and the Upper (?) Neocomian at Nettleton Hill.

It is this circumstance of the overlap of the Upper Cretaceous beds, combined with that of the Neocomian strata dipping at a high angle, which has caused these latter to occupy so small an area in Yorkshire.

At Speeton Cliff we have upwards of 500 feet of Neocomian clay exposed, although the upper part of the series is not here complete. Of the Upper Neocomian clays (above 150 feet thick) with the well-defined zone of the cement- beds, containing the remarkable fauna so exactly agreeing with that of the Atherfield clay of the South of England, no trace is discoverable inland, as they are completely covered up by the great drift-deposits of the Yale of Pickering.

The same is true of the Middle Neocomian (also 150 feet thick) with its well-defined fauna, marked especially by the abundance of the gigantic Pecten cinctus and the bands with numerous specimens of Ancyloceras towards its base.

Of the Lower Neocomian (200 feet thick) we obtain, however, distinct traces inland. After a very imperfect reappearance in Reighton Gill, only a mile from the cliff section (fig. 2), the upper- most beds (zone of Ammonites speetonensis) are quite lost under the drift for a distance of fifteen miles ; they are then seen again at West Heslerton, when on the very point of disappearing under the chalk in consequence of the overlap. The lowest beds of the Lower Neocomian are also found at Knapton, when about to be similarly lost under the Wolds.

The Neocomian beds, which thus disappear at Knapton, are entirely concealed from us by the overlapping Chalk strata for a distance of over forty miles (see Map, Pl. XXIII. fig. 3). In this space they have undergone considerable changes both in thickness and mineralogical characters ; but the several subdivisions are still recognizable by means of their characteristic fossils.

We have seen that the whole series of these beds in Yorkshire consists entirely from top to bottom of clays, varying, it is true, in such merely accidental characters as colour, amount of pyrites, the number and nature of the enclosed septaria, and the abundance and state of mineralization of their fossils. When, however, the Neocomian beds first reappear at Worlaby, in Lincolnshire, it is in the form of a coarse, greenish-white sand, in places passing into a hard sandstone. The deficiency and bad state of preservation of the fossils in these beds, which occupy the base of the Wolds from Worlaby to Clixby, prevents us from certainly deciding as to their place in the series. It is possible that they represent in a very