Final answer:
The excerpt expresses the idea of senseless destruction and exploitation in colonialism.
Step-by-step explanation:
The most clearly expressed idea about colonialism in this excerpt is the idea of senseless destruction and exploitation. The narrator observes the black people running and a detonation shaking the ground, but there is no visible change on the face of the rock. This suggests that the blasting is purposeless and that the construction of the railway is not serving any tangible purpose. The excerpt highlights the damaging and wasteful aspects of colonialism, where the indigenous people and their land are used and abused for the benefit of the colonizers.
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