Cooper relies on imagery to amplify the fact that Cora and Alice are foils. For example, in Chapter 1, he introduces Alice with light imagery:
The flush which still lingered above the pines in the western sky was not more bright nor delicate than the bloom on her cheek[...]
Alice appears from the very first as a "bright," "delicate," blushing young woman who reflects the light of a beautiful sunset. Her association with light underscores her innocence and softness, and also her whiteness. Cora, on the other hand, is more passionate than her sister. Where Alice defers to authority, Cora questions it. Where Alice repeats racist stereotypes she has heard, Cora challenges them. And where Alice plays the role of the damsel in distress, Cora plays a more active role in determining her own destiny—for instance, she refuses to save her own life by agreeing to marry Magua.
The novel chalks the sisters' differences up to their different mothers. Cora is revealed later in the novel to have distant Black ancestry, whereas Alice's mother was as white as the girls' father. Even before this revelation, Cooper introduces Cora in Chapter 1 with darker imagery that reflects the more violent sides of nature:
The tresses of this lady were shining and black, like the plumage of the raven. Her complexion was not brown, but it rather appeared charged with the color of the rich blood, that seemed ready to burst its bounds.
Cora can pass for white, but according to Cooper there is something more off-putting about her appearance than there is about Alice's. Alice is blond, but Cora's hair looks like the feathers of a scavenger bird. While Alice's flush is a "delicate bloom," Cora's is "the color of rich blood [...] ready to burst its bounds." In the antebellum United States, people could be legally classified as Black (and therefore eligible to be enslaved and otherwise subjugated) if they had a "single drop" of blood from a Black ancestor. Even if Cora's face doesn't immediately appear Black, Cooper's use of imagery makes it sound as though her non-white ancestry is waiting just beneath the surface, ready to "burst" out of her white-passing body.
Hawkeye and Duncan are foils, each representing a version of upstanding white masculinity that has been shaped by circumstance. The effects of their different upbringings is apparent in Chapter 19, when they discuss what might await each of them in heaven after they die:
“It is difficult to account for the feelings that may attend the last great change.”
“It would be a change, indeed, for a man who has passed his days in the open air,” returned the single-minded scout; “and who has so often broken his fast on the head-waters of the Hudson, to sleep within sound of the roaring Mohawk. But it is a comfort to know we serve a merciful Master, though we do it each after his fashion, and with great tracts of wilderness atween us [...]"
Hawkeye has told Duncan that he believes in heaven, but that he thinks it looks different for each person. He is not so sure that heaven for him would be a place of rest. Duncan suggests that his feelings might be different after he dies: both men seem to agree that death is the most mysterious of all human transformations. Hawkeye tells Duncan that spending his life "in the open air" has made the idea of barricading himself in a house and sleeping forever seem stifling. He concedes that both he and Duncan have the same "merciful Master," or God, but that they each "serve" Him in their own way.
This passage makes it clear that the "tracts of wilderness" between Hawkeye and Duncan are not just metaphorical, but also literal. Hawkeye came of age alongside Chingachgook and has dedicated his life to learning how to survive in the wilderness. Duncan, on the other hand, has grown up in European society. He has been indoctrinated into a different set of beliefs and practices, far from the heart of the forest. Each man's indoctrination has been so transformative that it has determined what his version of heaven will look like.
Given Hawkeye's repeated insistence that he is "a man without a cross," meaning in part that he does not belong to an organized religion, it is interesting that he tells Duncan that they share a "merciful Master." Cooper seems to be distinguishing between a belief in God and the practices associated with Christianity. Belief in God is inherent to Hawkeye's status as a white man. When he says he does not bear "a cross," he means that he is not bound by the rituals and customs Duncan has been bound to by his upbringing among Europeans.