Final answer:
The excerpt expresses the idea of exploitation and disregard for native people by the colonizers in colonialism.
Step-by-step explanation:
In this excerpt from Joseph Conrad's Heart of Darkness, the idea about colonialism that is most clearly expressed is the exploitation and disregard for the native people by the colonizers. The black people are seen running as a result of the detonation caused by the blasting for the railway. This objectless blasting symbolizes the meaningless destruction and disruption caused by colonialism without any beneficial purpose.
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