22
The Ancient Fauna of Essex.
in age with the Cyrena-beds of Grays, Erith, and Cray-
ford.
" Such being the case, so much of the Section No. 3,
given at p. 61 of the 'Geological Magazine,' 1866, vol. iii.,
as shows this brick-earth (x 4') underlying the gravel (x 4"),
is incorrect.......
"The subject, however, is obscure; and while the brick-
earth at Ilford, Grays, and Erith lies low, and forms a lower
terrace to the main sheet of the Thames gravel, it rises at
Crayford to a greater elevation, nearly eighty or ninety feet
in parts, and forms a high terrace above the gravel of the
Cray and Darent Valleys, but below the main gravel sheet
which forms Dartford Heath (see bed b of Section, fig. 9).
'' This anomaly and seeming contradiction is due in my
view to the reversal of the drainage during the progress of
the formation of the Thames Valley and the denudation of
the Weald, as discussed by me in my paper in the Quart.
Journ. Geol. Soc, 1871, vol. xxviii., p. 3."
In order to make the foregoing view more intelligible,
Mr. S. V. Wood has most obligingly prepared the accom-
panying Section13 (fig. 9), and adds :—
"Crayford is nearer to the region of Wealden elevation
than the other localities of the Cyrena brickearth ; and this
brick-earth has there been so elevated that the gravel of the
Cray and Darent Valleys (c of fig. 9) forms in places a very
distinct deposit occupying the valley-bottoms, and lying at a
level considerably below that of the Cyrena brick-earth.
This gravel e is, in my view, a deposit formed since the
drainage was reversed into its present direction; the Cyrena
brick-earth, on the other hand, having been deposited while
the drainage from the Thames Valley flowed into the sea
which covered the Weald. (See Section).
"I should, however, point out, as one of the perplexing
features of this obscure subject, that if we follow the gravel c
from the Cray and Darent Valleys to the edge of the Stone
Marshes, and crossing the Thames pursue it from its re-
appearance above the West Thurrock Marshes to the edge of
12 Fig. 9 is reproduced from Sir Antonio Brady's 'Catalogue of the
Pleistocene Vertebrata from the Neighbourhood of Ilford, Essex,' London,
1874. For other sections prepared by Mr. S. V. Wood to illustrate the
Geology of this area, see "A Day's Elephant Hunting in Essex," by Mr.
Henry Walker, F.G.S., with folding plate of lithographed sections, and two
woodcut sections on p. 32, Trans. Essex Field Club, vol. i., pp. 27—58
(September, 1880).