18 
A good deal of high land in the neighbourhood of the Kennet was 
covered with a deposit geologically called “ clay-with-flints,’” overlying 
which were brick-earths, intermingled with which, and lying in the 
clay-with-flints, Sarsens were often.found. Now, these beds always 
occurred in hilly ground, and in the upper chalk. In accounting for 
the presence of the Brickearths it would be necessary to consider that, 
at an early date, the stratified Eocenes, of enormous thickness in 
places, occupied an arctic sea, or rather two small inland seas, for 
such the so-named London and Hampshire Basins might be considered ; 
and that, by exposure to rapid currents, tides, and ice-floes, a large 
portion of the strata became denuded, leaving, as the waters shallowed 
by a gradual retiring of the land, masses of unstratified amorphous 
material over the face of the country. This same denudation left 
bare in places the Bagshot sands, London clay or Woolwich beds, as 
standing memorials of the wreck to which the Tertiaries had been 
exposed. This was succeeded by the scooping out of holes and pipes 
in the underlying chalk, which Sir C. Lyell and Mr. Prestwitch con- 
sidered must be due to the solution and carrying away of the chalky 
material by water, charged with carbonic acid gas, derived from the 
decomposition of the vegetable matter, which must have largely over- 
laid the surface. This process continuing would in time be the means 
of removing immense masses of chalk, the calcified water escaping 
down the pipes into the reservoirs and gullies permeating the chalk 
hills. ; 
At the time the pipes were forming the clay became precipitated 
into them, and mixing with the chalk-flints the whole graduated to 
the bottom, and formed the clay-with-flints. The Sarsens also dropped 
into the holes; and that portion of the clay which could not be 
absorbed into the clay-with-flints, remained on the top of the beds, 
and had been denominated Brickearth. Green and black-coated flints 
were not unfrequently found mingled with these deposits. Straggling 
pipes were further found in connection with these pot-holes, filled with 
coloured clay, derived probably from the decay of the chalk; and 
sand had also frequently worked'its way down into the pipes with the 
clay. During the time the sand-pipes were forming the clay, sand, 
and other materials had gradually become washed away, and channels 
formed in the superincumbent chalk, Then followed the snow, rain, 
and tempest of Mr. Tylor’s so-called “ pluvial period,” which tracked 
the footsteps of the sub-arctic period, and these persistent agents _ 
