is this a fungus? should I be worried?

In one of my borders about 2" below the surface I find what looks like a fungus that takes on the appearance of kitty litter.

The plants generally do well, although I have had some losses.

I do have cats that do poo in the garden and at times we do use it as a burial site for their kills (little monsters!!!) but this has been here since I moved in.

In the 2nd picture I have broken open the large lump you can see in the first picture

Does anyone know what this is?
Should I be worried?

I have moved plants from this area to another... am I spreading something terrible?

 

I'm thinking the technical term is Mycelium, its the fungus running though the ground and living on decomposing organic matter.
I've got large patches in my garden.

You might notice mushrooms/toadstools later in the year.

Never noticed it attack live plants and could even be good for the soil as it breaks down the organic matter into something that plants can use.

 

there were no 'shrooms that I could see last autumn.

Hopefully everything will be ok.. just not seen it before.

thanks