Pitlamp said:
Another useful source of information is to read material written by cavers who are known to have been consistently successful. As an example, in the post war period up to the 1960s there was a bloke called Les Salmon, who was very active in the Peak District. He was also a very good recorder of exploratory work (mainly in BSA publications but also elsewhere). More recent generations have focussed on outstanding work and promising leads flagged up by Salmon's writings, with many interesting finds resulting.
It all starts in the caving library
Funnily enough, I found a hilarious letter in the TSG library ages ago, between Trevor Ford and (I think) Les Salmon. They'd been sneakily digging at night in the Lower Bung Stopes in Speedwell, trying to get into what would now be the bottom of the Nameless Series, without success. They'd even more sneakily taken in some bang to help their efforts, and set off a charge at midnight or something. I think Trevor was still working at the Cavern at the time and the next morning he got a proper bollocking, as the fumes hadn't cleared in the streamway, but had blown back into the canal instead.
But agreed, there is still loads to find, even in areas considered 'played out', and digging is definitely worth it, if permission and logistics make it possible. That's the best part, finding something new. Pitlamp, your article in the 1991 Peak-Speedwell Cave Science mentioning the 'rule of thumb' about passage density/length between known entrances on a cave system (I don't have it in front of me) - the 10km of cave for every 1km separation - was that developed any further? It's certainly been useful to me, especially when looking at suspiciously 'empty' areas on the surveys of large cave systems