Many of his best works were, however, still to follow.

And, as regards imagination and the elements of mystery and awe, surely in the "Underground City" with its cavern world, its secret, undiscoverable, unrelenting foe, the "Harfang," bird of evil omen, and the "fire maidens" of the ruined castle, surely with all these "imagination" is anything but lacking.
From the realistic side, the work is painstaking and exact as all the author's works.

The sketches of mines and miners, their courage and their dangers, their lives and their hopes, are carefully studied.

So also is the emotional aspect of the deeps under ground, the blackness, the endless wandering passages, the silence, and the awe._ OFF ON A COMET OR HECTOR SERVADAC.