creepers. But I splashed on heedlessly – scarcely thinking to look around for any of the skulking man-lizards. In this open space I was not very likely to be waylaid. As I advanced, the light ahead seemed to grow in size and brilliancy, and I began to notice some peculiarity in its situation. Clearly, this was a crystal of the very finest quality, and my elation grew with every spattering step.
It is now that I must begin to be careful in making my report, since what I shall henceforward have to say involves unprecedented – though fortunately verifiable – matters. I was racing ahead with mounting eagerness, and had come within a hundred yards or so of the crystal – whose position on a sort of raised place in the omnipresent slime seemed very odd – when a sudden, overpowering force struck my chest and the knuckles of my clenched fists and knocked me over backward into the mud. The splash of my fall was terrific, nor did the softness of the ground and the presence of some slimy weeds and creepers save my head from a bewildering jarring. For a moment I lay supine, too utterly startled to think. Then I half mechanically stumbled to my feet and began to scrape the worst of the mud and scum from my leather suit.
Of what I had encountered I could not form the faintest idea. I had seen nothing which could have caused the shock, and I saw nothing now. Had I, after all, merely slipped in the mud? My sore knuckles and aching chest forbade me to think so. Or was this whole incident an illusion brought on by some hidden mirage-plant? It hardly seemed probable, since I had none of the usual symptoms, and since there was no place near by where so vivid and typical a growth could lurk unseen. Had I been on the earth, I would have suspected a barrier of N-force laid down by some government to mark a forbidden zone, but in this humanless region such a notion would have been absurd.
Finally pulling myself together, I decided to investigate in a cautious way. Holding my knife as far as possible ahead of me, so that it might be first to feel the strange force, I started once more for the shining crystal – preparing to advance step by step with the greatest deliberation. At the third step I was brought up short by the impact of the knife – point on an apparently solid surface – a solid surface where my eyes saw nothing.
After a moment's recoil I gained boldness. Extending my gloved left hands I verified the presence of invisible solid matter – or a tactile illusion of solid matter – ahead of me. Upon moving my hand I found that the barrier was of substantial extent, and of an almost glassy smoothness, with no evidence of the joining of separate blocks. Nerving myself for further experiments, I removed a glove and tested the thing with my bare hand. It was indeed hard and glassy, and of a curious coldness as contrasted with the air around. I strained my eyesight to the utmost in an effort to glimpse some trace of the obstructing substance, but could discern nothing whatsoever. There was not even any evidence of refractive power as judged by the aspect of the landscape ahead. Absence of reflective power was proved by the lack of a glowing image of the sun at any point.
Burning curiosity began to displace all other feelings, and I enlarged my investigations as best I could. Exploring with my hands, I found that the barrier extended from the ground to some level higher than I could reach, and that it stretched off indefinitely on both sides. It was, then, a wall of some kind – though all guesses as to its materials and its purpose were beyond me. Again I thought of the mirage-plant and the dreams it induced, but a moment's reasoning put this out of my head.
Knocking sharply on the barrier with the hilt of my knife, and kicking at it with my heavy boots, I tried to interpret the sounds thus made. There was something suggestive of cement or concrete in these reverberations, though my hands had found the surface more glassy or metallic in feel. Certainly, I was confronting something strange beyond all previous experience.
The next logical move was to get some idea of the wall's dimensions. The height problem would be hard, if not insoluble, but the length and shape problem could perhaps be sooner dealt with. Stretching out my arms and pressing close to the barrier, I began to edge gradually to the left – keeping very careful track of the way I faced. After several steps I concluded that the wall was not straight, but that I was following part of some vast circle or ellipse. And then my attention was distracted by something wholly different – something connected with the still- distant crystal which had formed the object of my quest.
I have said that even from a great distance the shining object's position seemed indefinably queer – on a slight mound rising from the slime. Now – at about a hundred yards – I could see plainly despite the engulfing mist just what that mound was. It was the body of a man in one of the Crystal Company's leather suits, lying on his back, and with his oxygen mask half buried in the mud a few inches away. In his right hand, crushed convulsively against his chest, was the crystal which had led me here – a spheroid of incredible size, so large that the dead fingers could scarcely close over it. Even at the given distance I could see that the body was a recent one. There was little visible decay, and I reflected that in this climate such a thing meant death not more than a day before. Soon the hateful farnoth-flies would begin to cluster about the corpse. I wondered who the man was. Surely no one I had seen on this trip. It must have been one of the old-timers absent on a long roving commission, who had come to this especial region independently of Anderson's survey. There he lay, past all trouble, and with the rays of the great crystal streaming out from between his stiffened fingers.
For fully five minutes I stood there staring in bewilderment and apprehension. A curious dread assailed me, and I had an unreasonable impulse to run away. It could not have been done by those slinking man-lizards, for he still held the crystal he had found. Was there any connexion with the invisible wall? Where had he found the crystal? Anderson's instrument had indicated one in this quarter well before this man could have perished. I now began to regard the unseen barrier as something sinister, and recoiled from it with a shudder. Yet I knew I must probe the mystery all the more quickly and thoroughly because of this recent tragedy.
Suddenly – wrenching my mind back to the problem I faced – I thought of a possible means of testing the wall's height, or at least of finding whether or not it extended indefinitely upward. Seizing a handful of mud, I let it drain until it gained some coherence and then flung it high in the air toward the utterly transparent barrier. At a height of perhaps fourteen feet it struck the invisible surface with a resounding splash, disintegrating at once and oozing downward in disappearing streams with surprising rapidity. Plainly, the wall was a lofty one. A second handful, hurled at an even sharper angle, hit the surface about eighteen feet from the ground and disappeared as quickly as the first.
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.
