LIST OF PLATES. 
I. Diagrammatic Sections across tlie outcrop of 
the Chalk in North Herts, showing relation 
of underground Water-level to the Wells and 
Springs, 1878-1888. To face p. 31 
II. Chart showing Water-level in Wells at Ther- 
field, Barley, and Odsey, on the 1st of each 
Month, with the Bainfall of each preceding 
Month [1878-1889] . Between pp. 36 & 37 
III. Map of Hertfordshire showing its Biver-Basins 
and Bainfall Stations .. « . .. Between pp. 80 & 81 
IV. Map of the Thames Basin showing the Bivers 
and Canals and the Area of the Chalk.. .. To face p. 129 
V. Plan and Section of Bennet’s End Brickfields, 
Hemel Hempstead.... . To face p. lxii 
