Answer: I would contend that the right answer is "There was nothing sufficiently pictorial about Irene's grief to stamp itself on his mind."
Explanation: Just to elaborate a little on the answer, it can be added that if Irene's grief was not powerful, striking, or rousing enough to move Dexter, this might be reflecting his heartlessness. As the narrator explains, the image of Irene suffering or in grief was not visually appealing enough to stamp or leave a mark on his mind, as another image would. A person who is not moved by another person's grief, and who can put words to his feelings in such a condescending and cold way, can be certainly described as cruel.
1-Nor did it matter that by his yielding he subjected himself to a deeper agony in the end and gave serious hurt to Irene Scheerer and to Irene's parents, who had befriended him.
2- There was nothing sufficiently pictorial about Irene's grief to stamp itself on his mind.
