London
One aspect of its geology had big consequences. North of the Thames London is on chalk, which is easy (with modern equipment) to tunnel through. South of the Thames London is on clay, which was, and still is, much more difficult to dig out. So most of the subterranean engineering is north of the Thames. The road system south of the Thames is also inadequate by modern standards. This difference is reflected in the prices for property, the road transport, the Underground railway and the definition of "London" as a taxable area. The growth of London has been more vigorous North of the Thames, and has included the complete absorption of Middlesex, once a separate county.