‘Oh, there you are!’ exclaimed Rick, as we emerged into a much larger chamber with huge boulders strewn everywhere.

‘Cobley held us up,’ I replied.

‘I was just about to come back,’ said Rick, sounding just slightly annoyed, but Nic went and whispered in his ear and he said no more about it. Cobley didn’t say anything at all!

‘Where have all these boulders come from?’ I asked. They were in the way, and we had to keep going round some, and over others, which made it hard work.

‘They’ve fallen down from the roof,’ Rick replied.

‘Not recently, I hope!’

‘Fairly recently’

‘What!’

‘Well, within the last thousand years, at a guess’

‘Rick!’ I exclaimed. ‘Are you trying to scare me?’

‘You’re the one with the grade ‘A’ in geography,’ he replied. ‘You know it isn’t that long, geologically speaking’

‘Yes, OK. But you made it sound as if they might have fallen down yesterday! We are safe, aren’t we?’

‘People used to die in caves,’ said Nic.

‘Nic!’

‘This part is pretty stable,’ Rick agreed, ‘but it can be a bit risky in active stream passages, especially ones that flood to the roof’

‘It doesn’t! Does it?’