Towards morning the ascending movement became accelerated. If the heat increased, instead of diminishing, as we approached nearer to the surface of the globe, this effect was due to local causes alone, and those volcanic. The manner of our locomotion left no doubt in my mind. An enormous force, a force of hundreds of atmospheres, generated by the extreme pressure of confined vapours, was driving us irresistibly forward. But to what numberless dangers it exposed us!
Soon lurid lights began to penetrate the vertical gallery which widened as we went up. Right and left I could see deep channels, like huge tunnels, out of which escaped dense volumes of smoke; tongues of fire lapped the walls, which crackled and sputtered under the intense heat.
"See, see, my uncle!" I cried.
"Well, those are
