File:The Quarterly journal of the Geological Society of London (13365623973).jpg

1850.. DE LA CONDAMINE — DISLOCATIONS AT ELACKHEATH. 44/
from it by the presence of imiierfectly rolled flints, which never occur
in the tertiary bed.
Thus we have a distinct line of demarcation between the Lower
and Middle Eocene periods, " during which," as Mr. Prestwich has
observed, " the water acquired greatly increased transporting power,
and after which the London clay was deposited in a more tranquil
and perhaps a deeper sea."
Fig. 4. — Section across Blackheath.
Horizontal scale 1 inch = 500 yards. Vertical elevation increased three times.
Observatory.
8 ,Si.\4S«W»WW,
1. Gravel.
2. London clay.
3. Pebble bed (No. 6).
4. Striped sandstone (No. 5)
5. Shell bed (No. 4).
6. Mottled clay, green sand and pebbles (No. 3).
7. Ash-coloured sand and flints (Nos. 1 & 2).
8. Chalk.
N.W
The date of the dislocation of these strata is posterior to that of
the partial denudation of the London clay. This will appear by
comparing the Map with the Section of the faults at Deptford. Be-
Fig. 5. — Section of the Lines of Dislocation at Deptford.
Horizontal scale 1 inch = 120 yards. Vertical elevation increased three times. S.E.
ii Reconstructed bed.
g 4 Fault. Faults.
1. Striped sand and loam (No. 5).
2. SheUbed (No. 4).
3. Mottled clay, green sand, and flints (No. 3).
4. Sandy loam.
5. Ash-coloured sands (No. 2).
6. Chalk.
tween the lines ah, cd Csee Map) there is a nondescript mass, which
tallies with none of the neighbouring strata, but which is just what
would result from the degradation and mixture of the striped sand.
No. 5, and the London clay. I therefore suppose the trough or
trench formed by the subsidence, real or comparative, of the original
surface between a h and c d (see figs. 5 and 6), to have been filled
up by the waste of the adjacent beds ; for had the London clay suf-
fered no denudation, it would occupy the space in question : whether
or not a remnant of it exists beneath the line of railway, remains to
be proved. This supposition is favoured by the indistinct basin-like
stratification of the sandy loam between h and d. There are also a
few pebbles in it, which may well have been derived from No. 6. I
have not however observed any fragments of the shell-bed.
The line of demarcation at d (see Section, fig. 5) is indistinct, the
edge of the fractured bed of sand. No. 2, having of course been soon
obliterated by the action of water. It is interesting to observe that
at 6, the tough strata of No. 5 bent before they yielded to the tension.