In Joseph Conrad's novel, Heart of Darkness, foreshadowing can be found in many places, not obvious until the story is finished and we can look back at the clues left for the reader.
I sense foreshadowing when Marlow hears that the Company has not heard from Kurtz in a long time. The only way they know he is still alive is because the ivory continues to be shipped out of the Inner Station. Of course, this is foreshadowing because communication would be something someone in their right mind would do to stay connected to the people for whom he works. However, Kurtz has become disconnected from civilization since entering the Inner Station. This is a clue of "darker" situations to come.
An example of foreshadowing is the satisfaction the company experiences as Kurtz continues to send back ivory. Something is obviously not right here in that communication has ceased from the Inner Station, but as long as the ivory keeps coming, no one seems extremely worried. This foreshadows the sense that human life has become of secondary concern to the members of the Company. And we see a perfect example of this truth when Marlow first enters the Lower Station to what he refers to as a vision of hell.
When Marlow arrives at the first station, the Lower Station, the condition of this station, which is the closest to civilization, is in chaos. The black workers have been enslaved: they are chained around the neck and then to each other. They have "the death-like indifference of unhappy savages." They are sick and starving. Some are beaten. Abandoned machinery is lying on the ground, like dead things rotting into nothing but rust. A group of men up on a cliff are blasting dynamite, as might be done to clear a road, but there is no earth to move for any imaginable reason, and yet they continue to blast.
The foreshadowing here is that if the Lower Station is so bad still so close to the civilized world, how can the Inner Station be anything but hell?—and it is, but in ways Marlow cannot even imagine.
At this point, it is important to mention the book's title, Heart of Darkness—here it begins to take on new meaning. At first it might refer to the jungle that is so dense as they begin their journey that the leaves appear black. As they travel up the Congo River, the darkness could apply to the densely shaded areas where the sun does not reach them: as they move ever deeper into that "darkness." However, when Marlow first sees the white guards and their treatment of the workers at the Lower Station, darkness within takes on a new meaning. This is foreshadowing—whether it applies to the men Marlow will meet on the journey, and/or to how Marlow might be touched by that darkness as well. While Kurtz has a "soul that is mad," Marlow admits there is something about Kurtz also that reverberates within Marlow, perhaps the same evil looking for some darkness in Marlow's heart.