1878.] 
335 
Superficial Gravels and Clays . 
Pisidium fontinale , var. Henslowana. 
,, amnicum. 
Unio pictorum and U . littoralis. 
Bythinia tentaculata and 5. Leachii. 
Hydrobia marginata, 
Valvata piscinalis and V. spirorbis. 
Planorbis complanatus and P. nautilens . 
Limnea peregra and L. truncatida. 
Succinea oblonga. 
Helix pulchella . 
Pupa marginata . 
Of the above shells the little Hydrobia marginata was the 
most abundant, though, from its small size, easily over- 
looked. 
Tio. 21. 
Section 30 yards South op Section shown in Fig. 20. 
s. Surface soil. a, i. Unstratified brown clay. a, 3; Gravel in clay. fl, 4. La- 
minated sandy clay or silt, with shells of Helix pulchella , H. capetata, and Zua 
lubrica. 
In some other pits sunk near this the subangular gravel 
(c in section) was much more developed, and the underlying 
shell-bearing sand confined to a thin drifted seam. One of 
the sections (Fig. 21) exposed was noticeable as the only one at 
which I obtained any shells in the Brentford district from beds 
belonging to the upper division. They occurred in a thin 
seam of sandy silt, occupying the same position in the series 
as the silt enveloping the buried forest near Ealing, already 
described. The most abundant shell in the silt was the little 
Helix pulchella , and no aquatic species were found. 
The gravels pass down below the Thames, and the bed of 
the river at Brentford is principally composed of reconstructed 
subangular gravel, with many shells of Unio , Anodon, 
Nerita , Pahidina, &c. 
I have the details of numerous other sections in my notes, 
all showing the same succession of beds, with the exception 
that I nowhere — excepting opposite Flora Villas-— saw the 
bed of dark yellow sand with Hydrobia marginata and Unio 
littoralis . The bed of sand with mammalian remains, 
