412
THE ESSEX FIELD CLUB.
In the introductory chapter Mr. Woodward describes the general geo-
logical structure of the district, pointing out the relations of the varions forma-
tions to each other. In the second he treats of the various subsoils, including
the "Made Ground," which cannot be ignored in towns of any antiquity.
In London, he tells us, it may be from a foot or two to about 25 feet in thick-
ness. "At the Bank of England there were 22 feet of" made ground "resting
on 4 feet of gravel." He remarks that "made ground" is not always an
unsatisfactory foundation for a house, though extremely objectionable when
it consists of rubbish containing a considerable admixture of animal and
vegetable refuse, which has filled a pit from which sand and gravel have been
taken. Then he notes the generally undesirable nature of alluvium as a site
for dwellings, and points out how large a proportion of old London and the
villages around it is built on tracts of the valley gravel of the Thames and
its tributaries. Other gravelly, sandy and sandstone sites are then considered,
also the "mixed subsoils" furnished by the Woolwich and Reading Beds,
the Valley Brickearth or Loam, and the Clay and Loam with Flints. Then
came the clayey formations. They consist of the Boulder Clay, London
Clay, Gault and Weald Clay. And lastly the one Limestone, known as the
Chalk.
Chapter III. consists of "General remarks on the subsoil with reference
to sites and foundations for houses." Mr. Woodward mentions the various
circumstances which need consideration in the case of gravelly, clayey, chalky
or other sites for houses. Chapter IV. contains remarks on Water Supply
and Drainage, some account being given of the various modes of supplying
London with water from an early period to the present day. Mr. Wood-
ward concludes with a short dissertation on Rural Water Supply and Sanita-
tion. Chapter V. is devoted to "General Sanitary Considerations in regard
to Situation and Surroundings of houses," and the concluding chapter deals
with the best sites for cemeteries.
Mr. Woodward's remarks on the various matters touched upon in this
memoir are the more valuable because he is always careful to point out all
the various circumstances which may tell for or against any given site, and
is far from looking at health as being a mere question of subsoil. A few
words on the admirable map accompanying this memoir may be useful,
especially to the non-geological reader, as the index to it shows primarily
the various beds as belonging to a sandy, gravelly or clayey series and not in
the order of their antiquity. The oldest formation within the limits of the
map is the Weald Clay, which is seen on the southern border from Dorking
eastward. Then adjacent to the Weald Clay, but north of it, came the Lower
Greensand, the Gault, and the Upper Greensand. North of them the Chalk
occupies a much broader belt of ground between Guildford and Gravesend,
and may be seen also in the north west corner of the map around Chesham.
The other beds shown are of very various ages but all of later date than the
Chalk. The letters and figures on the various formations mark their
relative antiquity. Thus on the Weald Clay may be seen "h 1," on the
Chalk "h 5," the beds between them being h 2, h 3, and h 4, according
to age. Similarly the lowest Tertiary series is that on which " i 1-2 "
appears, and so on; the post Tertiary beds not having any letter or
figure upon them at all. Then, to give clearness to the map, it has been
-ound desirable to reduce the number oi tints under which patches of