It's not really the geology that I was interested in (especially as knowledge of the cove has been improved since the 1940s when the book was written), more the anecdotes that the waterfall has formed more recently than 200 years ago, as reported elsewhere. Those accounts seem to indicate that the waterfall didn't reach the ground before disintegrating into spray, so the recent formation is perhaps the largest for quite a long time.
That's great Will. Any chance we can have the next page, you've left us hanging with the Charles Kingsley teaser?
I believe that when asked, Kingsley had said that the black streaks were formed by a chimney sweep falling from the top and dragging his brush down the cove as he went. Some time after this, he wrote his book "The Water-babies" which was apparently incredibly popular and tells the story of a young chimney-sweep, drowned after falling into a river. More here:
https://en.wikipedia.org/wiki/The_Water-Babies