tinct border along the landward
margins of the uplands of more ancient rock, though to the east of the
Cornwall-Devon peninsula it is not very clear, and its continuity in
other places is broken by inliers of the more ancient rocks, which
everywhere underlie it. One such outcrop of Carboniferous Limestone in
the south forms the Mendip Hills; another of the Coal Measures
increases the importance of Bristol, where it stands at the head of
navigation on the southern Avon. In the north-west a tongue of the Red
rocks forms the Eden valley, separating the Lake District from the
Pennine Chain, with Carlisle as its central town. Farther south, these
rocks form the low coastal belt of Lancashire, edged with the longest
stretches of blown sand in England, and dotted here and there with
pleasure towns, like Blackpool and Southport. The plain sweeps round
south of the Lancashire coal-field, forms the valley of the Mersey
from Stockport to the sea, and farther south in Cheshire the
salt-bearing beds of the Keuper marls give rise to a characteristic
industry. The plain extends through Staffordshire and Worcester,
forming the lower valley of the Severn. The greater part of
Manchester, all Liverpool and Birkenhead, and innumerable busy towns
of medium size, which in other parts of England would rank as great
centres of population, stand on this soil. Its flat surface and low
level facilitate the construction of railways and canals, which form a
closer network over it than in other parts of the country. The great
junction of Crewe, where railways from south-east, south-west, east,
west and north converge, is thus explained. South of the Pennines, the
Red rocks extend eastward in a great sweep through the south of
Derbyshire, Warwick, the west of Leicestershire, and the east of
Nottingham, their margin being approximately marked by the Avon,
flowing south-west, and the Soar and Trent, flowing north-east. South
and east of these streams the very similar country is on the Lias
clay. Several small coal-fields rise through the Red rocks--the
largest, between Stafford and Birmingham, forms the famous "Black
Country," with Wolverhampton and Dudley as centres, where the
manufacture of iron has preserved a historic continuity, for the great
Forest of Arden supplied charcoal until the new fuel from the pits
took its place. This coal-field, ministering to the multifarious metal