Can't say that I've been following this White Rock "debate", recently.
It's my guess that Alex doesn't know exactly what White Rock is, he could even take the position that it isn't "anything" in particular. I think his position is one of a skeptic, in that he sees no value in "jumping to any conclusion". If you can't provide evidence in which there can be "some degree" of confidence then there is little scientific value in forming a conclusion. The main part of Alex argument is that White Rock isn't "white"- though it certainly looks that way in pictures, and the reason for this appearance is the dark material surrounding it. And also Spectral analysis does not show that the "white rock" material is distinctive.
Now, it appears you have "moved on" by admitting White Rock isn't white and are trying to explain why the surrounding material is dark and reason has to do with "White Rock".
The whole point of being skeptical is avoid this type reasoning- you should build on what is "known"- instead jumping to some conclusion and "bending" everything to fit this conclusion. Now, there is nothing wrong with jumping to conclusions, it's just that you must be careful in finding evidence which supports it (and be prepared for others not to accept a conclusion unless there is enough evidence which supports it and also not let your bias affect your judgement.)
In other words, what evidence is there of there being different quantities of water associated with "White Rock" than compared with the surrounding region?