GEOLOGY The Oxford Clay and Kellaways Rock The Oxford Clay is now only represented by the lower beds within Northamptonshire ; it forms a fringe to the east of the county, from Yardley Chase to Peterborough ; patches of it occur as outliers at a few places (see map) ; it underlies part of the Fenland, and probably at one time covered the whole county. The formation, as here to be examined, consists of a blue, slate-coloured, or brownish clay when superficial, con- taining iron pyrites, selenite, septaria, and many fossils. The lowest portion, a little above the Cornbrash, is shaly, and contains fissile sandy layers almost passing into stone, with Avicula inaquivalvis, Gryphcea bi/obata, Nucula nuda, etc., and so no doubt represents the Kellaways Clay and Rock of other localities. The Kimeridge Clay to the Chalk There is some reason to believe that the Kimeridge Clay once covered the county, for its characteristic fossils occur rather abundantly in the Drift deposits at certain places, whereas traces of rocks of an age between it and the chalk do not. It is still more certain that the county was once covered with chalk, for the double reason that it could not have remained above water during the deposit of the deep sea chalk around, and the chalk and flint fragments of the early Drift are likely to have had a home origin. THE SCULPTURING OF NORTHAMPTONSHIRE On emergence of land subsequent to the chalk period the sculptur- ing of Northamptonshire began. Desiccation of the recently water- logged rocks caused their exposed surfaces to crack in all directions, while the gases of the atmosphere acted on them chemically. Possibly freezing and thawing, but certainly wetting and drying, and heating and cooling with night and day and the changes of the seasons assisted then, as they do now, in breaking up the surface of the ground, while wind and running water distributed the material. Assuming that denudation commenced here at about the same time that Tertiary deposits were beginning to be formed in the southern, south-eastern, and eastern districts of what is now England, we may consider that the sculpturing of the county has occupied between two and three millions of years. The dip of the newly-exposed ground determined the general, and inequalities on its surface the specific directions of the earliest main lines of drainage, but the deepening and widening of these primary valleys, and the development of lateral ones, has been chiefly the work of running water since. If we look at a map of the Catchment Basins of England, we shall observe that the Wash receives water from practically every point of the compass excepting that in which lies the open sea, which is at least inconsistent with the general south-easterly dip of the strata we 21
