ee —— 
, 
- 
J 
: 
SECTIONAL TRANSACTIONS.—C. 379 
Dr. J. W. Jackson and Dr. A. Butietp.~--The Occurrence of Corbicula 
fluminalis in the West of England. 
Recent excavations have exposed considerable sections of shelly sands and gravels 
in the vicinity of Middlezoy, Somerset. These beds, known as the Burtle Beds, 
contain a large series of common and widely-distributed marine shells, together with 
the bones and teeth of mammals. In the course of our researches we have had the 
good fortune to find a few examples of Corbicula flwminalis in these beds associated 
with the marine fauna. The latter is of a mixed facies, consisting of forms common 
to sandy, muddy and rocky habitats at the present day. The remains of the mammals 
are rather fragmentary, but we have been able to identify the following forms :— 
Elephas sp. (fragments of tusks), Rhinoceros sp., Bison or Urus, and Fallow Deer 
(strongly suggesting Cervus brownt). 
The occurrence of Corbicula fluminalis is interesting as being the first record for 
the West of England. It has been recorded from West Wittering, Sussex, along with 
similar marine shells to those obtained by us, and from the 80-90 ft. terrace of the 
Warwickshire Avon, at Ailstone, near Stratford. These are the two nearest sites to 
the Somerset locality. Thespeciesis known from the Red Crag and subsequent deposits 
up to the Middle Pleistocene at Crayford, where it makes its last appearance. It has 
been found in some abundance in the terraces of the Thames and Cam, and in the 
Oxford gravels ; also in the interglacial gravels at Kelsey Hill, Holderness, associated 
with numerous marine shells. In France it has been recorded from the estuarine 
bed, 24 feet above mean sea-level, at Menchecourt, where it occurred with seven 
species of marine shells identical with those found by us in Somerset. 
There is no evidence to suggest that the Somerset beds with Corbicula fluminalis 
are later than Crayford, which is regarded as Early Mousterian from its contained 
implements. 
The Burtle Beds have been assigned to two positions later than the Raised 
Beaches. One suggestion is that they were possibly formed during an early pause in 
the elevation of the beaches; the other that they were possibly formed during a 
pause at the termination of the subsiding movement which followed the elevation. 
The beds appear to us to be distinctly related to the Raised Beaches of the neighbouring 
coast, seen near Weston-super-Mare, being, in fact, the littoral sands deposited during 
the subsidence which closed with the formation of the beaches. During later elevation 
the Burtle Beds were ravined and their tops denuded, and on later subsidence the 
hollows were filled and the surface covered with alluvial and lacustrine deposits. 
The Raised Beaches, as is well-known, are overlain by aeolian sand, and that 
again by Head, the latter being regarded as representing the Magdalenian cold period. 
This suggests that the Raised Beaches may be Mousterian in age, as in the case of the 
Crayford Terrace of the Thames. It is interesting to note that Cervus browni is 
recorded with Corbicula from Clacton, which is slightly earlier than Crayford. 
Mr. F.W. AnvErson.—Phasal Deposition inthe Middle Purbeck Beds of Dorset. 
Many geologists have worked on the Purbeck strata since Webster’s account of 
these beds in 1816, and a large number of fossils have been collected by the various 
workers. The vertebrate fauna has been, for the most part, carefully described and 
figured, but the Mollusca are almost entirely undescribed. Further, owing to the 
nature of the deposits, lake and lagoon, rapid lateral change is the rule, and therefore, 
on lithological grounds also, only a very broad correlation has hitherto been possible. 
A study of the Ostracoda, however, combined with a microscopic examination 
of the beds in which the various forms occur, has demonstrated the existence of 
depositional phases, which being ultimately due to tectonic re-adjustment, should 
be of sufficiently wide application to allow of their recognition in other areas. 
Three phases may be recognised in the lower half of the Middle Purbeck. The 
- beginning of each phase is marked by fresh-water deposits, grey marls and shell 
limestones containing Paludina, Unio, Cyrena and fresh-water Ostracods. Throughout 
the phase there was a gradual shallowing of the water and increase in salinity ; towards 
the end deposition decreased and cherty limestones (shell breccias) are the typical 
_ deposit. Limnaea, Planorbis and Corbula are characteristic of this brackish water 
Stage. 
The increase in salinity had a marked influence on the Ostracod fauna. The 
fresh-water deposits at the commencement of each phase contain Darwinulaleguminella 
