We followed no road, but scrambled along over the open country, picking our way as best we could, and using the lights from the city to give us direction. The two girls half walked, half flew, and Mercer and I, with our ability to take huge leaps, made rapid progress.
The night was black—that unluminous blackness that seems to swallow everything, even objects near at hand. We made our way along, using little hand search‑lights that threw a red glare a short distance before us.
We kept down in the gulleys as much as possible, avoiding the higher places where Tao's long‑range beams were constantly striking, and passed around in front of the Dark City, keeping always at least five miles away.
We had been traveling two or three hours, and still Mercer and Anina gave us no clew to what we were about to see. It began to snow. Huge, soft flakes soon lay thick on the ground.
"Mercer, where are you taking us?" I exclaimed once.
"You shall see very soon now," Anina answered me. "What we have found, Ollie and I—and our plan—you shall understand it soon."
We had to be content with that. An hour later we found ourselves well around behind the Dark City and hardly more than four miles outside it. A great jagged cliff‑face, two hundred feet high perhaps, fronted us. We, at its base, were on comparatively low ground here, with another low line of cliffs shading us from the light‑beams of the city.
Mercer and Anina stopped and pointed upward at the cliff. A huge seam of the soft, chalky limestone ran laterally for five hundred feet or more across its face. I saw embedded in this seam great irregular masses of sulphur.
"There you are," said Mercer triumphantly. "Sulphur—stacks of it. All we have to do is set fire to it. With the wind blowing this way—right toward the city—" His gesture was significant.
The feasibility of the plan struck us at once. It was an enormous deposit of free sulphur. From this point the prevailing wind blew directly across the city. The sulphur lay in great masses sufficiently close together so that if we were to set fire to it in several places with our small light‑ray torches we could be assured of its burning steadily. And its fumes, without warning, blowing directly over the city—I shuddered as the whole thing became clear to me.