1 Heart cannot think what outrage, and what cries,

Heart > Mind

2 With foul enfouldred smoke and flashing fire,

enfouldred > {?As black as a thunder-cloud. SU; cf. 202.20:9}

3 The hell-bred beast threw forth to the skies, 4 That all was covered with darkness dire:

That > [So that]

5 Then, fraught with rancour and engorged ire,

fraught > filled engorged > swallowed; hence: internal, swelling, choking

6 He cast at once him to avenge for all,

cast > decided, resolved him > [himself] for all > [once and for all]