NOTE ON THE GEOLOGY OF THE BOBBITSHOLE AREA, IPSWICH by P. G . H . BOSWELL, D.SC., F . R . S . ,
F.G.S.
THE discovery by Mr. H. E. P. Spencer of the Bobbitshole interglacial deposits has not only added greatly to our knowledge of the plant and animal life of the time, but also furnished another example of the disturbance of the local strata caused by the Gipping valley glacier as it made its way southwards during the Ice Age. Like the well-known examples of glacial disturbance in other Suffolk Valleys, situated at positions where spurs from the plateau projected into them or steep bluffs faced upstream, it helps to prove that the main valley-systems of the district were carved out before the latest ice-advance*. The most striking of these disturbances were described, it will be remembered, by the late Dr. George Slater between 1907 and 1927, mostly in the Proceedings of the Geologists' Association of London. The nearest large-scale examples were those of the Hadleigh Road Railway cutting and neighbouring building excavations, the Dales brickfield and the Claydon chalk-pit, where strata ranging from the Chalk to the glacial deposits, were folded, thrust and sheared and often inverted as a result of having been frozen as dirt bands in the lower layers of the advancing ice. In Dr. Slater's experience these examples of englacial disturbance, which threw much light on glacial tectonics, were as remarkable as any that he or other authorities had described from elsewhere in the world. In the Bobbitshole district the disturbance appears to have been on a smaller scale, but Mr. Spencer's acute Observation caused him to record anomalous dips of the strata and their abnormal levels. It might well have been predicted that this was a locality where disturbance would be found. Among the Eocene deposits which have recently been recorded as occurring in the neighbourhood are the Oldhaven Beds. In Kent, these beds lie between the Woolwich Beds and the London Clay and are distinguished by a characteristic fossil assemblage. Until the early part of this Century, the Oldhaven Beds were said to occur in Suffolk but when their molluscan fauna came to be carefully worked out, this Statement proved to be incorrect. The deposits that were mistaken for them were the pebble-beds, clays * " O n t h e Age of the Suffolk Valleys ; with Notes on the Buried Channels of D r i f t . " Quart. J. Geol. Soc., London, v. 69, 1913, pp. 581-618.
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and sands which lie at the base of the London Clay*. They were found to be fossiliferous at many localitie's, the most rewarding of which was that in thelower part of theDales brickfield, north-east of Ipswich. Here the molluscan fauna showed that the deposits belonged to the basement-bed of the London Clay. The recent declarations that the Oldhaven Beds occur in Suffolk have not been accompanied by statements of the evidence in support.
* " T h e Stratigraphy and Petrology of the L o w e r E o c e n e D e p o s i t s of the N o r t h - E a s t e r n Part of the L o n d o n B a s i n . " Quart. J . Geol. Soc., London, 1916, v. 71 (for 1915), p. 568.
NEW FROM
SUFFOLK RIVER
MAMMALIA
GRAVEL : BARHAM
B y HAROLD E . P . SPENCER,
F.G.S.
Just over one hundred thousand years ago the Gipping Valley was deeper than it is now, and the geography of Suffolk probably differed much from that of to-day. It is evident the amount of water flowing was much greater then and great quantities of gravel which had originally resulted from the melting of the ice of the third glaciation was transported by the rapidly moving water. Possibly much of the water feil during torrential storms which caused floods where many of the animals which normally grazed or browsed in the valley bottoms were drowned. Their remains are often found in river terrace gravels.