254 Preston: Geology South of Grantham. 
great. When rain falls and sinks into the ground it percolates 
through the fissures of the rock until an impervious surface 
is reached, and the water then travels as a sheet along’ this 
surface in the direction of the dip. -If a section of the pervious 
and impervious rock now be cut at right angles to the dip, as is 
often done in railway cuttings, the water will ooze out along ‘the 
juncture of the two beds. When such sections are forme 
naturally, as in the case of the Witham Valley before us, the 
water may find a little easier outlet at one point than another, 
which by degrees is enlarged into a spring, and water rushes 
out more or less copiously. This is what has occurred in the 
case before us. The Witham Valley has formed the section 
cutting into the Lias Clay, and at the junction of beds there are 
two large dip springs called the Hovel Spring and Adam’s Well, 
and marked ¢ and d in plan, Fig. 1. Now all this water cannot 
ooze out and rush out from between a clay and sandstone or 
limestone without gradually bringing away, particle by particle, 
some of the two rocks, the upper surface of the clay, and the 
under surface of the limestone, or, in this case, sandy bed. This _ 
action is chiefly a mechanical one, and is greatest near the outlet, 
S 
Hence, I believe, the peculiar valley-like openings crossed in the 
pipe trench are fractures caused by the letting down of the 
limestone rock due to the scouring action of the two springs, 
the Hovel Spring and Adam’s Well. The sands have been 
gradually washed out, much of the lower bed of limestone has 
been dissolved by carbonated water, and some of the upper 
surface of clay has been removed in the course of time, with the 
result that the limestone mass has gradually settled down to itS 33 
bed, causing strain and ultimate fracture along the upper surface. 
Granting the first crack, denudation by percolating carbonated 
water will vied account for subsequent widening and for 
ee the rubbly sides of the fissures. 
re, then, we have an area recording its own history of 
destruction and change, and giving us facts which may be well 
used in explaining the past history of the Lincolnshire cliff, and 
possibly also of the great gorges in that cliff at Honington and 
L 
incoln, 
On our return journey we shall have an opportunity of 
passing down a very picturesque valley in the limestone between 
Neoseek and: A Littte Ponton. ‘The valley is not marked on the on the — 
! ‘ Naturalist, 
( 
