Muck/dirt along joist under bathroom floor

[snadge]

I have pulled down ceiling in Kitchen to replace and found something running along joists from waste downpipe - it looks and feels like soil - its dry and only seems to have travelled along the joist, first obs would be that its from the waste downpipe, whats others thoughts and advice?

see pics below

thanks

 

[Nige F]

soil from that leaking soil pipe

 

[snadge]

soil from that leaking soil pipe

thing is, its dry - not damp - do u think it could be an OLD leak? - the ceiling we took down seemed to be slightly soft and warped under there...

sorry, I know its so obvious its a leaky pipe but sometimes i like reassurance and others input on it - its not leaking anymore and is dry