Confidence: It's likely to be this, but I can't be certain.
Notes: Frankly I was going to ignore this, but I am reluctant to leave it as a 'Peltigera', which it is not. Nevertheless, Hilary's suggestion is very reasonable, given the lack of habitat information. Hilary interprets the photo as showing earth, but I think it is bark? We SHOULD be told! The photograph itself is not sharp and so gives little information. I don't think a firm ID is possible, but this looks very like the sort of chewed (mites, bark lice?) scraps of Parmelia, usually P. sulcata, that one sees on trees where growth conditions (pollution, low humidity) are pretty poor. Ideally it would have white flecks ('pseudocyphellae') on the surface, which I cannot make out here, but they are often not well developed on scrappy material. Sorry to be critical Mick, but you generally take much better photographs of much better material than this! I don't think it is anything exciting.