What created this Sherlock?

This is a piece of Delabole slate, buried millennia ago during construction of the land mass. It appears that a creature was in mid-flow building a home when suddenly the lights went out.

To the right is what appears to be an entrance hole, top left there appears to be an access tube and left of that another access hole. The "nest" area comprises a honeycomb lattice which is quite substantial, I think it is made from reconstituted stone or mud.

The whole piece is 15cm wide, 5 cm high and 1.5cm deep. Any ideas what could have created this?

Use Sherlock's magnifying glass.

It seems that the growths are crystals formed between layers of sedimentary slate, the slate has been pressurised and become metamorphic, according to the Fossil Forum. I thought I'd made a discovery. Bummocks. :-))