The answer is slime mould.
You might think that slime moulds, also known as members of the group Mycetozoa, are fungi. In fact, they did use to be classified as such but it is now recognised that fungi and slime mould are unrelated.
Autumn is a good time to see slime mould. And, of course, you can see them at Dove Stone. One of the really interesting things about slime moulds is, in the life cycle stage known as plasmodium, they move ! During this stage slime moulds are feeding on bacteria, spores and other organic matter.
Four of the most common slime moulds are Fuligo septica ( known attractively as Dog's vomit slime mould ), Enteridium lycoperdon and Lycogala terrestre ( feeding mostly on dead and rotting wood ), and Mucilago crustacean ( feeding on grasses ).
At some point in relation to the availability of food slime moulds leave the plasmodium stage of their life cycle and, resembling the appearance of fungi, go on to release spores to reproduce, at which point the life cycle starts over. Fascinating stuff. Many thanks to Ken for suppying us with some fantastic photos of slim moulds.
For those interested here is a link to a really quite amazing film of slime moulds made by John Bonner:
http://www.youtube.com/watch?v=bkVhLJLG7ug