At the Earth's Core by Edgar Rice Burroughs

When our guards aroused us from sleep we were much refreshed. They gave us food. Strips of dried meat it was, but it put new life and strength into us, so that now we too marched with high-held heads, and took noble strides. At least I did, for I was young and proud; but poor Perry hated walking. On earth I had often seen him call a cab to travel a square -- he was paying for it now, and his old legs wobbled so that I put my arm about him and half carried him through the balance of those frightful marches.

The country began to change at last, and we wound up out of the level plain through mighty mountains of virgin granite. The tropical verdure of the lowlands was replaced by hardier vegetation, but even here the effects of constant heat and light were apparent in the immensity of the trees and the profusion of foliage and blooms. Crystal streams roared through their rocky channels, fed by the perpetual snows which we could see far above us. Above the snowcapped heights hung masses of heavy clouds. It was these, Perry explained, which evidently served the double purpose of replenishing the melting snows and protecting them from the direct rays of the sun.