How does Cooper present Major Heyward and the Munro sister? Why does Cooper add David Gamnut to their party? How does he first appear? How can we tell they are out of place in the enviroment they must tranverse?

Last question first, the women are completely out of their environment, which is one of the reasons they so foolishly and thoughtlessly demand to continue with their journey. Cooper introduces the women in order to create suspense, something he immediately succeeds at, even if we as readers shake out heads. There is also a detailed description of the women......something we learn more about later; they are sisters but very different.

As for Gamnut, he's almost a distraction. The only reason he's allowed to jolin the group is because of Alice's persuasion.

Further information can be found at gradesaver's chapter summary cited below;