Sounds like resin from the tree, Margaret. Are there lumps of amber like substance on the branches? Normally there is nothing to worry about though you may want to replace the discoloured stones with bark.

It may also be honeydew from a bad case of aphids, but I would expect more of that in spring, when the new growth is at its peak.

It is a beetle ... the name escapes me ... aargh! When conditions are warm enough the beetles hatch and suck the resin from the tree. They then produce a sticky sweet black/purple sap (loved by ants) ... much like aphids do. I had this on a christmas tree (spruce type) three years ago. Brought it indoors for christmas and two days later the floor was covered with this sticky sap, and then loads of spider-like beetles everywhere. When squashed they left a purple sap. Local nursery told me what it was, but cannot for the life of me find it now. Have tried to google. When I remember the name of this beetle I will let you know. Ultimate Bug Killer comes to mind as this will ravage any new conifer growth in your area.

Thanks for answers but no sign of aphids or lumps on the tree, in fact the tree has never looked healthier, so im hoping it stays like that, maybe I will just turn the stones over and hope for the best.