The Charing Cross, Euston & Hampstead Railway (CCE&HR) ran from CC to Golders Green and also to (what is now known as) Archway. Odd that we have found plaques at Tufnell Park and Belsize Park which were never the termini of the line. Do plaques exist at other stations as well?
In 1912 it was extended south to Embankment. Then in the early 1920s, delayed due to WW1, it was integrated with the City & South London Railway (C&SLR) which had opened in 1890, forming something close to that many-headed monster of a line that we now know as the Northern Line.
Londonist have a good post about the Northern Line's history with great pictures.
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