What parts of Joseph Conrad's Heart of Darkness show foreshadowing?

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.