DE RANCE : UNDERGROUND WATERS IN LINCOLNSHIRE. 33 
The Upper Estuarine Series is 35 feet in thickness at Lincoln, 
and thins northward to 15 feet at Ancholme Head. They consist of 
clays, sandy clays, and sands, that are generally impermeable, form- 
ing an impervious barrier between the waters of the Lincolnshire 
(Oolite) Limestone and the Great Oolite Limestone. A hard sand at 
the base of this series yields water at a depth of 49 feet below the 
platform at Potter Handworth Station, blue and red clays, with jet 
and bands of pyritous sandstone occurring above. The latter are 
a great feature of this series, and the decomposed pyrites produces 
an acidity of soil as deleterious to vegetation as to purposes of water 
supply. Strong clays of this age occur at Xettleham, Dunholme 
Lodge, and Gorse Cover, between Welton and Hackthorn, and 
support a sheet of water in the Great Oolite. 
The Great Oolite Limestone is a compact shelly ragstone, its 
average thickness is 15 feet, though water-bearing, its small area and 
thickness render it of little importance for a public supply. The 
water rising to the surface near Dunholme Church in the Kellaway 
Rock, lying at the base of the Oxford Clay, may be derived from 
Great Oolite or Lincolnshire Limestone ; both are penetrated by a 
boring 106 feet deep on the west of the village. 
At Honeyholes Farm a pond receives the water from the roof of 
a large barn. It is situated on a soft sandy clay, doubtless belonging 
to the Boulder Clay Drift. The vegetation changes, and ditches are 
seen in the area overlaid by the Boulder Clay, and on the outcrop of 
Upper Estuarine series. Deep-set ponds occur south of Honeyholes, 
but they only contain surface water. 
The Great Oolite Clay is an impermeable dark bluish deposit 
about 25 feet in thickness, and occasionally used for the manufacture 
of bricks, as at Metheringham Station. 
The Cornbrash is a thin-bedded shelly limestone, of a rusty 
colour above and of a deep blue below, it is compact and crystalline 
and only five feet in thickness ; for water supply purposes it is of no 
importance. 
The Kellaway Beds consist of a few feet of black shales at the 
base, overlaid by the Kellaway sands, the junction being well seen in 
