Formation of petrified trees
But I don't understand the part of "degradation action" in the question, I think underground water only replaces the plant material in trees...


Degradation refers to the process of aqueous dissolution of the organic materials; the fact is, organic materials are generally quickly dissolved after the death of a living organism...degraded into nothing before the fossilization process can even start. (Think of the carbon cycle and how organic compounds are re-used over and over again over the eons of life on this planet.)

It's a bit of a misnomer in this case because it ignores the simultaneous replacement of that organic matter with inorganic siliceous materials.