Quick visit to this cave yesterday, needs another visit.
Although there is a public footpath leading to the cave, this is not straightforward, first finding the start took some time (look for the public footpath sign with "not coast path" scratched on it). The last part of the path once had ladderways etc but these have now gone so is now a short scramble which is certainly not granny friendly.
The cave starts with a large sea cave, with a colony of fulmars in & around it, probably best avoided in the nesting season both to avoid disturbance & to avoid the wonderful defense mechanisms those birds have!
The cave resurges a fairly significant stream; at the back of the sea cave is a steep & unstable climb up above which there appears to be a largish continuing passage or chamber.
There is also an adit close by, shown on 1:2500 maps, but didn't manage to get there due to rising tide.

Hi Ali,
Is this cave in Granite, Killas or Greenstone?

Further details would be helpful for when I am next down with the wife's family (they live quite near Mousehole).

After yesterday's post looked at the most recent 1:2500 OS which shows a depression with a cave symbol near the coast road. This is no doubt the sink for the stream. It is labelled "quarry" on the first edition OS (ca 1877). This suggests that a stream cave has formed on the boundary between the granite & overlying head deposits (which contain generally in West Cornwall granite areas are largely made of granite boulders). Will try to put a photo of the cave on my facebook page.
Incidentally put a couple of survey legs in & getting the magnetic variation from the BGS site resulted in a negative correction - is this a first for a cave survey in the UK?
see http://britgeopeople.blogspot.co.uk/2014/01/somethings-happening-to-magnetic-north.html

A return visit showed that the slope up at the back is very unstable, steep unconsolidated sand & boulders. I would only try & ascend further by bolting the left handwall so when the slope goes you don't go with it. There is a strong draught. According to local information it used to be possible to do a through trip, but there were several accidents so the council blocked the top entrance (which we havn't yet been to). Also local rumours that when this done a Spanish suit of armour was discovered! all we found was a very large rusty spanner. Noted on the north wall of the main entrances hitches have been cut in the past perhaps for a substantial walkway into the cave.