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CHAPTER X. 
DEPOSITS OF DOUBTFUL AGE. 
In the previous Chapters most of the British Pliocene strata 
have been described. There remain, however, a number of 
deposits which undoubtedly belong to some part of the series, 
but have not yet yielded evidence sufficient to fix their exact 
horizon. There are other strata of more doubtful age, though 
probably pre-glacial. We have also still to trace the connection 
between the Pliocene beds and the overlying glacial deposits. 
Owing to the uncertain age of so many of the outliers, the only 
classification that can be adopted in the present Chapter is a 
geographical one. We will commence, as a matter of convenience, 
with the area in which the series appears to be most complete. 
In the last Chapter the Ci’omer Forest-bed, with its prolific 
fauna and flora, was described. It was shown that this deposit 
clearly belongs to the Pliocene period ; though perhaps to a very 
late stage of it. Above the Forest-bed, but beneath the oldest 
known Glacial deposit, there are sands and gravels, sparingly fossi- 
liferous, and of still unsettled age. These strata between Bacton 
and Sherringham, include two distinct series—a marine bed 
characterized by Leda myalis, and a freshwater or flood deposit 
with Arctic plants. It is only in a few localities that either 
of the horizons is fossiliferous ; and in the absence of fossils the 
separation of them from each other, and from the underlying 
Forest-bed, is a matter of considerable difficulty. 
The marine deposit overlying the Forest-bed at West Runton 
has been known for many years, but its exact relation to the 
Crag and to the Glacial Beds is still an open question. The 
name Leda-myalis Clay ” was first used, as a local term applied 
to this section, by Prof W. King in 1863,"^ and it has since been 
adopted for the horizon between the Upper Freshwater Bed of 
the Forest-bed Series and the Arctic Freshwater Bed. At 
present very little is known about its fauna, for the deposit is 
sparingly fossiliferous ; but the fossils that do occur are generally 
found in colonies in the position of life. It is this stratum that 
has often, though erroneously, been correlated with the Bure 
Valley Beds, and has led some to place the Norwich Crag over 
the Forest-bed. 
The Leda-myalis Bed usually consists of fine false-bedded 
loamy sand with grains of Chalk, thin seams of loam or clay, and 
* Geologist, vol. vi., p. 160. 
