Rye and Derwent Drainage. 



♦133 



level, called the Vale of Pickering, in length about 25 miles and 

 in breadth about 8 miles, and containing an area of not less than 

 160 square miles.* It consists of a clay vale formation, technically 

 called the " Kimmeridge clay." Its general structure is a thin 

 alluvial covering, and a variable thickness of diluvial pebbles and 

 clay upon a bed of thick blue clay. It is bounded on the north 

 by the Yorkshire Moorlands, the basis of which is oolite lime- 

 stone, dipping to the south, and upon which the clay vale forma- 

 tion lies, and on the south by the Yorkshire wolds of chalk, 

 under which the valley clay runs, and towards the west by the 

 Howardian hills of oolite. These ranges of hills meet together, 

 or nearly so, at the east end, near Filey on the coast ; and at the 

 west end, near Helmsley, the hills also meet together and equally 

 close the valley in that direction. The only outlet for the 

 drainage of this wide plain is at Malton, on its south side, and 

 nearly equidistant from its extremities, and, fortunately, towards 

 this point the substratum of clay, which forms the basis of the 

 valley from the north, east, and west, somewhat inclines in a 

 basin form. The natural drainage is carried on by the rivers 

 Rye and Derwent, which both arise at the summit of the moor- 

 lands, at the opposite ends of the valley, and run a course of not 

 less than 40 miles, each receiving many large tributary streams, 

 descending from the moorland dales, which open into the main 

 valley. About three miles above Malton, very nearly in the 

 centre of the vale, the Rye and Old Derwent unite and become 

 one river ; the Derwent, which runs in a south-west direction, 

 and, passing through a ravine of dislocation through the oolite 

 rocks at Kirkham, gains the vale of York, discharging its waters 

 into the Ouse, meeting the tide-water of the Humber at a dis- 

 tance of about 27 miles below Malton. The general level of 

 the valley is about 60 feet above the sea, and the lowest level 

 at Yeddingham Bridge only about 35 feet ; and were this valley 

 at Kirkham closed up, the vale of Pickering would become, what 

 there is little doubt it once was, an extensive lake, discharging 

 its water into the sea at Filey. 



The artificial obstructions placed upon these rivers were as 

 follows : — At New Malton, on the Derwent, was a mill men- 

 tioned in Doomsday Book ; another at Old Malton, a mile higher 



* The annexed plan is only intended to represent generally the geological 

 formation of the district— the topography and the number and extent of the rivers 

 and streams ; it was desirable also to have represented the contour lines of the land 

 actually flooded and injured; but it was found impossible, on so small a scale, to 

 reduce the boundaries of the assessed lands— they must therefore be imagined to 

 occupy a narrow space spreading generally along the margins of the rivers and 

 streams, extending to the level of 4 feet above the highest flood marks, and in 

 several places, particularly at the confluences of the streams, forming basins of 

 considerable extent. 



