File:The Quarterly journal of the Geological Society of London (13205900435).jpg

PITTON S SECTION AT ATHERFIELD.
Fig. 3. Fig. 4.
mm
291
Black- Gang Chine.
Whale and Walpen Chines.
Vndercliffs. — The picturesque scenery at the back of the Isle of
"Wight, emphatically called " the UndercliiF," is a most striking ex-
ample of the structure, or rather destruction, produced by the alterna-
tion of solid or permeable strata with others more retentive of moist-
ure. In the present section, some cases occur of less prominence, but
not undeserving of notice. Looking eastward, from the top of the
cliif, near Atherfield, towards Rocken End, the strata are seen to rise
conformably at a very small angle of inclination ; but their uniformity
is broken by two or three less regular shelves, and these upon exami-
nation are found to have been produced by certain retentive beds
among the looser strata. The water thus kept up carries off a part
of the lower mass, undermining that above ; and the result is the pro-
duction of a shelf or terrace, between two ranges of cliffs, one of them
supporting " the Undercliff," the second forming a remoter vertical
face behind.
Six or seven of these minor undercliffs formerly existed on the
coast between Atherfield and Rocken End, one of which (near Ather-
field) has now nearly disappeared. The most remarkable of those
which remain is due to a group of clay and retentive sand, in which
Captain Ibbetson was the first to discover several species of fossil
shells, and which is for the greater part concealed by ruins of the
upper strata. The underclifP upon this clay rises nearly at Walpen
Chine, ascending westward and crossing Ladder and Whale Chines.
Another marshy undercliff, which comes down to the shore on the
east of Cliff-End, has been produced by the fall of the white sand and
clay No. 41, a small portion only of which is visible near Walpen
High-cliff : and still other alternations of clay and sand in the beds
above have cooperated with the Gault in producing the fall of the
upper greensand, by which enormous masses of that deposit have
been brought down, even to the sea-side, at Rocken End.
Divisions of the Section.
The whole series of deposits here consisting of sand and clay, with
great uniformity of aspect, the most obvious divisions might be derived
from their difference in mineral composition. The list of strata which
I have adopted is therefore in some measure arbitrary, and intended
chiefly to facihtate reference to this particular section ; and I cannot
too strongly caution my reader against supposing that similar sub-
divisions of groups, which in a geological sense are the same, are to
be expected in other places, especially when the distances are great.
It will presently be seen that within the Isle of Wight itself, the