I now summoned up all my strength and prepared to throw a third handful as high as I possibly could. Letting the mud drain, and squeezing it to maximum dryness, I flung it up so steeply that I feared it might not reach the obstructing surface at all. It did, however, and this time it crossed the barrier and fell in the mud beyond with a violent spattering. At last I had a rough idea of the height of the wall, for the crossing had evidently occurred some twenty or twenty-one feet aloft.
With a nineteen – or twenty-foot vertical wall of glassy flatness, ascent was clearly impossible. I must, then, continue to circle the barrier in the hope of finding a gate, an ending, or some sort of interruption. Did the obstacle form a complete round or other closed figure, or was it merely an arc or semi-circle? Acting on my decision, I resumed my slow leftward circling, moving my hands up and down over the unseen surface on the chance of finding some window or other small aperture. Before starting, I tried to mark my position by kicking a hole in the mud, but found the slime too thin to hold any impression. I did, though, gauge the place approximately by noting a tall cycad in the distant forest which seemed just on a line with the gleaming crystal a hundred yards away. If no gate or break existed I could now tell when I had completely circumnavigated the wall.
I had not progressed far before I decided that the curvature indicated a circular enclosure of about a hundred yards' diameter – provided the outline was regular. This would mean that the dead man lay near the wall at a point almost opposite the region where I had started. Was he just inside or just outside the enclosure? This I would soon ascertain.
As I slowly rounded the barrier without finding any gate, window, or other break, I decided that the body was lying within. On closer view the features of the dead man seemed vaguely disturbing. I found something alarming in his expression, and in the way the glassy eyes stared. By the time I was very near I believed I recognized him as Dwight, a veteran whom I had never known, but who was pointed out to me at the post last year. The crystal he clutched was certainly a prize – the largest single specimen I had ever seen.
I was so near the body that I could – but for the barrier – have touched it, when my exploring left hand encountered a corner in the unseen surface. In a second I had learned that there was an opening about three feet wide, extending from the ground to a height greater than I could reach. There was no door, nor any evidence of hingemarks bespeaking a former door. Without a moment's hesitation I stepped through and advanced two paces to the prostrate body – which lay at right angles to the hallway I had entered, in what seemed to be an intersecting doorless corridor. It gave me a fresh curiosity to find that the interior of this vast enclosure was divided by partitions.
Bending to examine the corpse, I discovered that it bore no wounds. This scarcely surprised me, since the continued presence of the crystal argued against the pseudo-reptilian natives. Looking about for some possible cause of death, my eyes lit upon the oxygen mask lying close to the body's feet. Here, indeed, was something significant. Without this device no human being could breathe the air of Venus for more than thirty seconds, and Dwight – if it were he – had obviously lost his. Probably it had been carelessly buckled, so that the weight of the tubes worked the straps loose – a thing which could not happen with a Dubois sponge-reservoir mask. The half-minute of grace had been too short to allow the man to stoop and recover his protection – or else the cyanogen content of the atmosphere was abnormally high at the time. Probably he had been busy admiring the crystal – wherever he may have found it. He had, apparently, just taken it from the pouch in his suit, for the flap was unbuttoned.
I now proceeded to extricate the huge crystal from the dead prospector's fingers – a task which the body's stiffness made very difficult. The spheroid was larger than a man's fist, and glowed as if alive in the reddish rays of the weltering sun. As I touched the gleaming surface I shuddered involuntarily – as if by taking this precious object I had transferred to myself the doom which had overtaken its earlier bearer. However, my qualms soon passed, and I carefully buttoned the crystal into the pouch of my leather suit. Superstition has never been one of my failings.
Placing the man's helmet over his dead, staring face, I straightened up and stepped back through the unseen doorway to the entrance hall of the great enclosure. All my curiosity about the strange edifice now returned, and I racked my brains with speculations regarding its material, origin, and purpose. That the hands of men had reared it I could not for a moment believe. Our ships first reached Venus only seventy-two years ago, and the only human beings on the planet have been those at Terra Nova. Nor does human knowledge include any perfectly transparent, non-refractive solid such as the substance of this building. Prehistoric human invasions of Venus can be pretty well ruled out, so that one must turn to the idea of native construction. Did a forgotten race of highly-evolved beings precede the man-lizards as masters of Venus? Despite their elaborately-built cities, it seemed hard to credit the pseudo-reptiles with anything of this kind. There must have been another race aeons ago, of which this is perhaps the last relique. Or will other ruins of kindred origin be found by future expeditions? The purpose of such a structure passes all conjecture – but its strange and seemingly non-practical material suggests a religious use.
Realizing my inability to solve these problems, I decided that all I could do was to explore the invisible structure itself. That various rooms and corridors extended over the seemingly unbroken plain of mud I felt convinced; and I believed that a knowledge of their plan might lead to something significant. So, feeling my way back through the doorway and edging past the body, I began to advance along the corridor toward those interior regions whence the dead man had presumably come. Later on I would investigate the hallway I had left.
Groping like a blind man despite the misty sunlight, I moved slowly onward. Soon the corridor turned sharply and began to spiral in toward the centre in ever-diminishing curves. Now and then my touch would reveal a doorless intersecting passage, and I several times encountered junctions with two, three, and four diverging avenues. In these latter cases I always followed the inmost route, which seemed to form a continuation of the one I had been traversing. There would be plenty of time to examine the branches after I had reached and returned from the main regions. I can scarcely describe the strangeness of the experience – threading the unseen ways of an invisible structure reared by forgotten hands on an alien planet!
At last, still stumbling and groping, I felt the corridor end in a sizeable open space. Fumbling about, I found I was in a circular chamber about ten feet across; and from the position of the dead man against certain distant forest landmarks I judged that this chamber lay at or near the centre of the edifice. Out of it opened five corridors besides the one through which I had entered, but I kept the latter in mind by sighting very carefully past the body to a particular tree on the horizon as I stood just within the entrance.
There was nothing in this room to distinguish it – merely the floor of thin mud which was everywhere present. Wondering whether this part of the building had any roof, I repeated my experiment with an upward-flung handful of mud, and found at once that no covering existed. If there had ever been one, it must have fallen long ago, for not a trace of debris or scattered blocks ever halted my feet. As I reflected, it struck me as distinctly odd that this apparently primordial structure should be so devoid of tumbling masonry, gaps in the walls, and other common attributes of dilapidation.