17th June 2009, 05:24 PM
From the description it sounds like a couple of bits of "slag" I found on our local disused railway line many years ago*. Pale bluee crust about 1cm thick with vesicular material on what I assume was on the inside. I always assumed it was slag used as ballast when laying the lines (some of the other ballast material I recall was vesicular grey stuff).
* by "many" it was probably about 35!
* by "many" it was probably about 35!