langcliffe said:Pitlamp said:Langliffe - dunno - but next time you're up there maybe quietly chip a tint bit off and see what the fresh fracture looks like? (With your geological knowledge I'm sure you don't need further explanation.)
We did that a couple of weeks ago - it certainly looked like it. I was just thinking that if anybody else could confirm it, then it would a good place for those interested to see what it looks like.
I finally got round to having a look at this t'other day. I wasn't entirely sure which boulder you mean - but if you walk up-dale from the turn off to Braida Garth there are six boulders in a line along the verge on the right. (These boulders are clearly seen on Google Earth.) The final one, immediately before the long layby on the right, is classic porcellanous limestone. It's got the characteristic calcite "fenestrae" and has several pretty fresh surfaces, allowing it to be easily identified with a geological hand lens (but without having to knock it about with a hammer).
So yes - great point Langliffe - if anyone wants an easy location to view porcellanous limestone, this fits the bill.