What's this, chaps?

[Fergie 307]

it could be saltpeter its normally found in cellars used to make gunpowder is the only use i no its used for and i mean proper black powder gunpowder

I think in the old days it was more commonly sourced from the floors of "outhouses".
The Salt Petre men were even known to dig up the floors of churches. Apparently because people were known to relieve themselves on the floor during a long and boring sermon.
Guano is also a good source and was shipped in large quantities from islands with large bird populations.

 

[shavings&sawdust]

As above, crunchy/crispy it's salt, soft/furry it's fungal/mould, if it's mould do NOT use bleach to try remove it, you'll supercharge it and it will rapidly spread everywhere.

Salt should dissolve in water, mould doesn't. Had outside wall repointed and could 'harvest' buckets of salt from inside in the very dry attic the following year.