Jack London approaches to narration styles by speaking of the thoughts of the main character (mostly dogs). While G. A. Henty usually shows character development by letting the main character have dialogues with others.
Also, they have different Setting descriptions. Jack London loves to descriptively set up a scene before he walks you through what happens while G. A. Henty likes to show you the setting as you go by reading what happens.
Jack London and G. A. Henty also have different Character development approaches. Jack London likes to show you the important parts of the animals life. G. A. Henty shows the Character development by working things in chronological order, unlike Jack London.
Jack London and G. A. Henty both have very different writing styles.