I like stuff like this: Does The Northern Line Extension To Battersea Mean The End Of The Kennington Loop?
He's certainly an enthusiastic fella for all things trains and tube that Geoff Marshall. You have to admire his dedication.
at a tangent, when the northern line was still two separate lines, the southern terminus of the charing cross, euston and hampstead railway, at charing cross (now embankment) was also a loop - the northbound platform at embankment was the terminus hence being on a bloody tight curve. the bit of line under the thames was plugged at each end during WW2 to prevent risk of flooding due to bomb damage article and photos here by some 'guerilla explorers'
