The two peaks might correspond to the dual nature of Charles' nationality -- English and Costaguanero -- that the novel plays on elsewhere. Certainly this moment inaugurates his Costaguanero career.

Hats are also a shade, and shade in Nostromo is symbolic of whatever ideal or expedient shields a person from disillusioning reality. In this scene -- so heavily laden with symbolic sunlight -- Charles' two-peaked hat could symbolize his youthful idealism, his mature idealism and this, the implicit valley between.