1878.] 
337 
Superficial Gravels and Clays. 
more southern species, Cyrena fluminalis . In higher beds at 
Brentford, and mixed through the lower part of the gravel, 
I found a more robust form of Unio pictorum than occurs in 
the lower sands, along with a peculiarly thick form of Cyclas 
rivicola, but without any of the two southern shells. Prof. 
Morris, in the description of the beds near Kew Bridge, in 
which he found numerous remains of the reindeer, states 
that he could not find a fragment of Cyrena fluminalis, Unio 
littoralis, or Hydrobia marginata, although the northern spe- 
cies of mollusks were abundant. 
The sandy subangular gravel lying above the mammal- 
iferous sands is simply a continuation of that found at higher 
levels at Ealing. It only differs in containing more sand at 
the lower levels, and occasionally drifted shells and bones. 
The largest stones lie at the bottom of the gravel, as in the 
Ealing district: : they consist of slightly worn flints, and 
more or less rounded stones of quartz, quartzite, and sand- 
stone. At low levels — that is, below the 30-feet contour-line— 
bones of mammals are often found in this gravel, especially 
when, through the denudation of the older sands, it lies 
direCtly on the London Clay. These bones have been derived 
from the older beds. Mr. Trimmer states that the remains 
he found were most abundant at the base of the gravel, in 
hollows in the London Clay, where the deposit consisted of 
a heterogeneous mass of clay, sand, and gravel. In no in- 
stance, he states, have two bones been found together which 
were joined in the living animal. That the gravel is largely 
mixed with the pre-deposited sands is evident from the 
patches of the latter that occur in it full of the comminuted 
shells that are found uninjured in the undisturbed beds. 
Excepting these derived shells I have never seen any in the 
subangular gravel. 
Passing on to the beds lying above the subangular gravel, 
we have again a most remarkable resemblance in the colour, 
composition, and succession of the deposits to those I have 
grouped under the same symbol in the Ealing district. In 
both cases the beds consist of unstratified brown clay, con- 
taining a few pebbles scattered throughout it and overlying 
patches of pebbles. Below the latter there are, occasionally 
preserved, remnants of a silty clay, in which I have found 
land shells near Brentford, and remains of a buried forest 
bed near Ealing, as already described. The brick-clay appears 
originally to have covered the whole district, but has been 
removed over much of the area from ancient brick-fields, 
the limits of which may still be traced by the abrupt slopes 
left at their boundaries. 
VOL, VIII. (n.s.) 
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