I am quoting from the Return of Sherlock Holmes, The Missing Three Quarter by Arthur Conan Doyle :
"Yet even without knowing his brilliant record one could not fail to be impressed by a mere glance at the man, the square, massive face, the brooding eyes under the thatched brows, and the granite moulding of the inflexible jaw. A man of deep character,a man with an alert mind, grim, ascetic, self-contained, formidable—so I read Dr. Leslie Armstrong. He held my friend’s card in his hand, and he looked up with no very pleased expression upon his dour features."
First of all I don't understand the usage of the word 'moulding' and I don't understand the point of the metaphor in this sentence, does he mean that the character is silent that's why is jaw doesn't move, I mean who doesn't move his jaw it doesn't make sense. can you explain this please?