Many were the mad and impossible schemes that my fevered brain formed for making an attack on the flaming brain of metal, only to reject each upon consideration. As I had hurtled through the air above the pit, in my ill-starred attack in the Omnimobile, I had been much impressed by the narrowness of the bridge of cliffs between the great lake and the abyss. Now it occurred to me that I might dig a canal, and let the waters of the lake in to flood the Lord of Flame. With that in mind, I made an expedition to the isthmus, armed with copper pick and spade. I found that my eyes had curiously deceived me, from the air. The land bridge was a wall of rock, nowhere less than a hundred feet high and four hundred thick, covered with a rank growth of jungle. Along it, even as Xenora had said, was a ruined road. Here and there a crumbling stone monument rose from the jungle like a bleached skull of the dead civilization. There was no hope of digging a canal. A hundred men, in ten years, might have been able to cut a tunnel through that wall of stone, with modern tools and explosives! Nitroglycerine! That started me on a new line of thought. I had once made chemistry a hobby. It was not impossible. For Sam, it would have been child's play. But, alas! there was no help from my old friend! I set to work at once. For many months I labored. The task was a tremendous one. The first necessity was an adequate supply of nitrates. I was not fortunate enough to discover a natural deposit, as heroes of fiction usually are; so I set out to make a "nitrate plantation" such as is used for the manufacture of nitrates in a primitive way. I dug a great shallow pit, lined it with waterproof clay, and filled it with alternate layers of wood ashes obtained by burning the purple trees, and everything I could pick up in the way of nitrogenous animal and vegetable refuse. At last it was filled and wet down with water from my clay-bed. I had nothing to do but wait until the nitrogen products of decomposition had united themselves with the potassium bases in the wood ashes. Then I fell to the mining of iron pyrites, and to the building of a furnace in which I could burn my pottery apparatus. After many disheartening failures I was able to set up apparatus that I thought would suffice for the manufacture of my acids. I burned rude jars, glazed with sand, in which to carry and store my reagents and explosives. My memory of all that time is a dim dream of terror. Many times for long hours I stood on the brink, gazing into the flickering mist, thinking of Xenora and half determined to give it all up and to seek her. But always I went back to my mad task, toiling in a daze of grief and despair.