I'll have to find out where I read that. I think I read it in an excellent autobiography on him a few years ago (I can't look it up in the book as I lent it to someone but never had it back). Google doesn't provide much answers either. In fact, it suggests the opposite!
On second thoughts, I think it was more of a statement regarding that looking at mountains, despite his love of nature and the like, didn't "inspire" him in the often romanticised interpretation of the word, he wasn't "stirred-up" after looking at a mountain.
Damn, I'll have to buy a another copy of the book (I really hope that it was in there that I saw it!):
Also very interesting, particularly in the context of this discussion, is what one of the reviewers says: "I understand now why I couldn't understand his writing: Mr. Thomas often chose words for their SOUND rather than MEANING. We search for MEANING where there is none"