The Tyne rises in two branches. The North Tyne begins in the Cheviot Hills in Northumberland
and the South Tyne in Cumberland
below Cross Fell. The two branches join about two miles above hexham and flow for about 30 miles to the North Sea
. The lower stretch of Tyne marks the boundary between Northumberland
and is of great commercial importance. Newcastle Upon Tyne
is the most important city along its banks.