This appears to be a largely silicified oolitic ironstone or oolitic ironstone breccia. Swarms of sub-parallel dark brown fractures give the impression of wood grain.
Comments:
There is no clear evidence that this was wood, and so the specimen more correctly belongs with Corsi's 'diaspri' (jaspers).
References:
Further information:
Corsi's classification:
Class 14. Quartz and its varieties; Species 3. Petrified wood