of motor-traffic. Following the Roman
roads, the high roads of the Eastern Division very frequently run
along the crests of ridges or escarpments; but in the Western Division
they are, as a rule, forced by the more commanding relief of the
country to keep to the river valleys and cross the rougher districts
through the dales and passes. The railways themselves, radiating from
the great centres of population, and especially from London, are only
in a few instances much affected by configuration. The Pennine Chain
has always separated the traffic from south to north into an east
coast route through the Vale of York, and a west coast route by the
Lancashire plain. The Midland railway, running through the high and
rugged country between the two, was the last to be constructed. The
most notable bridges over navigable water affording continuous routes
are those across Menai Strait, the Tyne at Newcastle, the Severn at
Severn Bridge and the Manchester Ship Canal. It is more usual to
tunnel under such channels, and the numerous Thames tunnels, the
Mersey tunnel between Liverpool and Birkenhead, and the Severn tunnel,
the longest in the British Islands (4-1/2 m.), on the routes from
London to South Wales, and from Bristol to the north of England, are
all important. The Humber estuary is neither bridged nor tunnelled
below Goole.

_Density of Population._--The present distribution of population over
England and Wales shows a dense concentration at all large seaports,
in the neighbourhood of London, and on the coal-fields where
manufactures are carried on. Agricultural areas are very thinly
peopled; purely pastoral districts can hardly be said to have any
settled population at all. There are very few dwellings situated at a
higher level than 1000 ft., and on the lower ground the Chalk and the
Oolitic limestones, where they crop out on the surface, are extremely
thinly peopled, and so as a rule are areas of alluvial deposits and
the Tertiary sands. But, on the other hand, the broad clay plains of
all formations, the Cretaceous sandstones, and the Triassic plain, are
peopled more densely than any other district without mineral wealth or
sea trade.

_Political Divisions._--In the partition of England and Wales into
counties, physical features play but a small part. The forty ancient
counties, remnants of various historical groupings and partings, are
occasion