To this discovery succeeded some others equally mortifying. (Chapter 6)

He thought more highly of his abilities. The discovery related directly before the above citation is that Darcy misjudged Lizzy’s facial features. IMO Darcy is mortified because he finds his judgment of Lizzy’s appearance was wrong. The rest of the other equally mortifying discoveries compare his original judgment of her form and manners against his revised judgments of them. I do not see anything in the citation from Chapter 6 which indicates Darcy is now mortified by his behavior at the assembly or his treatment of Lizzy and he certainly does not go on to act on such a sentiment, lets say by apologizing to Lizzy which a repentant person might do when confronted with the revelation they have wronged someone. IMO Darcy is simply mortified that his judgment was wrong; his vision of his ability to judge has been shown to be less than accurate. :)