Rock Diver

The leitmotif of the story is a journey to the center of the Earth^[10]: 120 in search of valuable raw materials^[11]: 160 through the use of technology allowing penetrating or passing through matter.^[12] Harrison wrote that he based the story's outline on a classic Western plot and the idea of claim jumping, but repackaged it with a sci-fi setting.^[13]: 81

The story was one of the early science-fiction works describing the effect of penetrating or passing through matter^[12] although Harrison himself admitted that the idea for such a device was not his and he was inspired by prior science fiction works.^[13]: 81 Algis Budrys in 1967 in the context of the anthology Science Fiction Inventions, where the story was reprinted, wrote that it was "a real landmark SF story, in the special sense that each of them either originated or first fruited a basic technological idea in such a happy combination with story values that it is impossible to touch that idea again without having to find some totally new framework for it”.^[14]: 126 Likewise, in 1985 Jerry Pournelle noted that the story "had the kind of idea that immediately engages the SF addict".^[15]: 19 Brian Stableford listed it as one of "notable accounts of burrowing expeditions" into Earth that are relatively consistent with the knowledge of modern geology.^[16]: 138

A reviewer for Analog Science Fiction and Fact wrote in 1969 that it is "highly realistic yarn about prospecting and claim-jumping inside the Earth. This could be the ultimate development of the old gimmick of the man who can walk through walls."^[11]: 160

Lech Jęczmyk wrote that many consider this to be Harrison's best story, due to the original idea ("not the cosmos, not the ocean, but the earth's crust as an area of conquest") and the story itself being "an engaging drama".^[17]