Its a slime mould, on a wet log. Looking around the internet, it may be Lycogala terrestre (Wolf’s Milk) rather than the very similar Lycogala epidendrum but its hard to tell. It seems we were lucky because they turn brown pretty quickly.
Slime moulds have been described as ‘amoeba with attitude’ which sounds about right. No point reinventing when someone else has done the hard work, so here is a nice clear description from the btweenblinks blog
They are neither plant nor animal. Slime molds were once regarded as fungi, but are now classified in an entirely different kingdom called Protista which includes algae and protozoans.
In their initial phase of life, they are small amoeba-like single celled organisms which spend their time searching for bacteria and fungus to eat. When a significant number exist, they join together to form a fruiting body in what is called the plasmodium stage. During this phase they can still move, but only at a pace of approximately 1 mm per hour. When they run out of food, they dry up and release their spores. These spores begin the whole life cycle again.
Loads of lovely slime mould photos on Flickr which show what an amazing variety of forms there are. And the many strange uses to which they can be put.