Sticking Tufa into google gives some amazing limestone formations in the US, nothing like that in the valley containing Stoney Littleton unfortunately.
http://www.monolake.org/naturalhistory/tufa.htm
http://en.wikipedia.org/wiki/Tufa
Were the pits further up the valley then, I'd love to see a complete archeological map of that valley and the next one over towards Faulkland. My question, is where is the Causewayed Enclosure that goes with the barrow at Wellow and the circle at Faulkland? :)