114 THE ESSEX NATURALIST.
until, late in 1924, the requisite depth was reached. Since then
the section has changed but little, and appears at present as
follows :—
3. Bagshot Sands.
2. Passage Beds.
1. London Clay.
Fine-grained sand of pale buff
colour, showing bedding on a minute
scale, and with grey clay bands at
intervals .. .. .. .. 14ft.
Rapid alternations of sand and clay
in bands averaging 2ins. in thickness,
resting conformably but with a
sharp junction on the beds below.
14ft.
Stiff black shaly clay 2ft.
Thin band of glauconitic
sand . . .. .. 4ins.
Greenish sandy clay .. 8ft.
Stiff black clay (base
not seen) .. .. 5ft.
——15ft. 4ms.
1. The London Clay shows its normal lithology as displayed
in many sections near London. Fossils are found throughout
the lower black clay, although, as usual, there is some tendency
for them to occur in bands. They are- not pyritized, and have
suffered crushing and shearing during the accommodative
movements of the clay mass, whose nature is attested by numerous
slickensided joint and bedding-planes. The larger lamelli-
branchs are especially difficult to remove.
The greenish sandy clay above is also fossiliferous, but the
fossils have largely been removed by interstratal solution. The
upper few feet of the London Clay here have yielded nothing
to prolonged search, though, as noted above, fossiliferous Septaria
occur at this horizon. There is definite evidence that some at
least of these Septaria are still forming by simple segregation of
calcareous matter in the body of the clay. White ovoid patches
may be observed in the section, which, whilst they are still as
soft as the surrounding clay, are undoubtedly incipient nodules.
In one case the whitish material was found to contain 16% of
calcium carbonate, while the surrounding clay was practically
lime-free. These facts are worthy of notice, for, in other localities,
the Septaria appear to be penecontemporaneous, having been
bored by marine organisms, while they lay on the sea bottom.
Moreover, Mr. Wrigley has observed elsewhere the accumulation