This fan-shaped accumulation of bouldery gravel is marked in the
geological survey maps as covering a space of about two square miles south
of Pickering, but the deposit is probably much larger, for Dr. Thornton
Comber states that the gravel extends all the way to Riseborough and is
found about 6 feet below the surface, everywhere digging has taken place
in that direction. The delta is partly composed of rounded stones about 2
feet in diameter. These generally belong to the hard gritstone of the
moors through which Newton Dale has been carved. Dr. Comber also mentioned
the discovery of a whinstone from the great Cleveland Dyke, composed of
basaltic rock, that traverses the hills near Egton and Sleights Moor, two
miles above the intake of Newton Dale at Fen Bogs.

The existence of this gravel as far towards the west as Riseborough,
suggests that the delta is really of much greater magnitude than that
indicated in the survey map. It has also been proved that Newton Dale
ceased its functions as a lake overflow, through the retreat of the
ice-sheet above Eskdale long before the Glacial Period terminated, and
this would suggest an explanation for the layer of Warp (an alluvial
deposit of turbid lake waters) which partially covers the delta. The
fierce torrents that poured into Lake Pickering down the steep gradient of
this canon would require an exit of equal proportions, and it seems
reasonable to suppose that the gorge at Kirkham Abbey was chiefly worn at
the same time as Newton Dale.

[Illustration: Diagrammatic view showing the presumed position of the ice
at the eastern end of the Vale of Pickering during the Lesser Glacial
epoch. The river Derwent is shown overflowing along the edge of the
glacier.]

Another delta was formed by the upper course of the Derwent to which I