File:The Quarterly journal of the Geological Society of London (13071265604).jpg

94
PROCEEDINGS OF THE GEOLOGICAL SOCIETY. .Jan. 9,
traces of rolling, the most minute processes and the most delicate
ridges being as perfect as in the day when they dropped from
the decaying carcases swept down by the current. They are
therefore in exactly the same position as when they originally
dropped from the stranded or floating animal, and are not derived
from any preexistent mammalian deposit — a very important fact
in determining the palseontological age of the beds.
Other pits have been opened in the same layer of Brick- earth in
the neighbourhood of Ilford, and have afforded vast quantities of
remains to the cabinets of collectors for the last fifty years. Most
of them are now closed. The Mammalia which are in Dr. Cotton's
collection were obtained from one of these pits at a depth of 15 feet
below the surface, or from the same horizon as the head of the Mam-
moth indicated in my section (fig. 1).
Fig. 2. — Section at Mr. Pearson's Pit, Grays Tlmrrock.
Surface-soil, 3 feet.
"Trail," from 3 to 4 feet.
False-bedded sands, and lenticular gravel-beds, 10 feet.
G-rey laminated clay, with seam of gravel, 4 feet.
Lenticular mass of shells.
Laminated grey and reddish clays, interstratifled with sand and gravel,
14 feet.
Sand and gravel, 10 feet.
. llfi .' Chalk.
/3. Grays Thurrock. — The Brick- earths at Grays Thurrock are
situated on the north bank of the Thames, about 12 miles to the east
of those at Ilford. The summit of the ground at Mr. Pearson's por-
tion of the large brickfield is about 40 feet above the level of the
alluvium, from which it is separated by a low bank of gravel ; on the
north side it abuts against the Thanet Sand ; and at the point where
the section (fig. 2) is taken it rests directly on the chalk, occupy-
ing an area about one mile long and a quarter of a mile broad, between
Grays and Little Thurrock. On the north side of Mr. Pearson's pit
the following section is presented : — Immediately on the top of the
chalk is a deposit of sharp sand and gravel (No. 1), consisting of sub-
angular and rounded flints, with a few pebbles of quartz, and contain-