SECTIONAL TRANSACTIONS.—C. 313 
additional protection of a partly submerged reef known as Christchurch Ledge. The 
strata composing the Barton Clay pass out to sea in a south-easterly direction. 
Extensive banks of shingle, however, have accumulated west of Highcliff and 
near the entrance to the rivers Stour and Avon which have a common outlet to the 
sea at Cliff End. Thus it is doubtful whether the lower sections of Barton Beds will 
again be available for investigation, because they are partly overgrown, and the sea 
no longer washes the base. Further east, a large number of ironstone concretions 
must lie at the bottom of Christchurch Bay. These concretions have been removed 
from the Middle Barton Beds between Highcliff and Barton Court, and they may 
often be seen scattered in profusion along the shore-line during certain states of the 
tide. These Septarian concretions were formerly taken away by boat, for ballast, 
but as this practice was considered to result in more rapid wasting of the cliffs, the 
Lord of the Manor forbade the practice. 
Three divisions are recognised in the Barton Beds: Lower, Middle, and Upper 
Barton. The thickness of the Lower Barton is put at 49 feet, and the thickness of 
the Middle and Upper Barton at 53 and 90 feet respectively, making a total of 192 
feet. In the Isle of Wight the total thickness reaches 338 feet at Alum Bay, and 368 
feet at Whitecliff Bay. The most remarkable variations are seen in the Middle 
Barton at Alum Bay (167 feet) and the Upper Barton at Whitecliff Bay (221 feet). 
The horizons are distinguished partly by their lithological character, and partly by 
the fossil remains. 
The lowest limit of the Upper Eocene has generally been taken at the Nummulites 
elegans zone, 10 feet above a layer of rolled flint pebbles imbedded in sand. The 
boundary line between Middle Eocene and Upper Eocene is somewhat doubtful. 
Numerous casts of bivalves and a few gastropods occur in the highest part of the sand, 
as also among the rolled flints, but they might be referred to either series. The best 
preserved fossils are the fir-cones, Pityostrobus dixoni, found in the green clay above 
the flints, and remains of Chelonia are occasionally met with. We may assume from 
the evidence here, that the Barton Beds commenced their initial stages in shallow 
water, and that subsequently the water deepened, giving us the truly marine beds of 
the Barton Clay proper. The sand drifts in the higher part of the Lower Barton 
contain about 400 species, many of which are very minute. Apart from these local 
accumulations, the deposits of Lower Barton age appear singularly barren. The 
term ‘ Highcliff Sands,’ applied to indicate these (lower) beds, is misleading, and ° 
would be better employed for the Bracklesham sand near Cliff End, west of Highcliff. 
The Upper Bracklesham facies of the marine fauna is noteworthy and persists even as 
high as the Pholadomya Bed which marks the base of the Middle Barton Beds. 
Fossils of the Barton Clay are usually in perfect preservation, but slight lateral shifting 
of the beds during upheaval or chemical alteration in the bed itself has been 
responsible for the fracture or destruction of a number of otherwise fine examples of 
marine mollusca. Mollusca, sharks’ teeth, and also bone remains are sometimes 
completely encrusted with a ferruginous deposit in the lower parts of the Barton Clay. 
Taking the beds in ascending order, it will be noticed that specimens from Lower 
Barton closely resemble those of the ‘ Brook Bed’ in the New Forest, and that those 
found in the glauconitic sandy clay of the Middle Barton are compressed or other- 
wise distorted, as at Bracklesham Bay in Sussex. 
Higher up, we come to more compact brown and grey clays, in which the shells 
are splendidly preserved, every spine and lineation being most perfectly retained. 
Finally, the Chama Bed of Upper Barton, which consists of a bluish grey sandy clay, 
contains rather delicately preserved bivalves and six species of Volutes. This is 
followed by the generally unfossiliferous Barton Sands, and, last of all, the dark hard 
sandy clay of the Becton Bunny Beds (Oliva branderi Zone) and the Long Mead 
End transitional bed at Hordle, which bed is the highest member at present attributed 
to the Barton Series in Hampshire. The fauna undergoes a marked change from the 
Middle Barton type. 
The more tropical aspect of the Middle Eocene (Bracklesham) fauna seems to 
justify the arrangement of the British Eocene in three divisions, instead of only two. 
The temperature of the sea was lower when the Barton Clay was laid down, and this 
induced the withdrawal of the larger Cones and Cowries, as well as the huge Cerithia 
and most of the Bracklesham Volutes. Paleontological changes are, however, more 
abrupt between Middle and Upper Barton than they are between Bracklesham Beds 
and Lower Barton. Species characteristic of the Barton Beds are Pleurotoma rostrata, 
Volutilithes ambiguus, and Conus scabriculus. 
