Chemical weathering would cause the inscription on a marble gravestone to become harder and harder to read overtime. I am hoping that this answer has satisfied your query and it will be able to help you in your endeavor, and if you would like, feel free to ask another question.
Umm... Well, I am not the best in this type of subject, but I believe it would be chemical weathering or weathering. Chemical weathering, like acid rain, degrades stone down until either the rain stops or the stone is gone.
