Four starts in as many different directions and twenty minutes of time showed fairly conclusively that the line of vegetation which had given rise to the "street" theory was growing along a straight crack, apparently a fairly ordinary joint, in the limestone. While several more holes would have to be drilled to prove it, even Mitsuitei was willing to admit that in all probability the remaining lines would be found to be over similar cracks.
"You must admit, though, that the regularity of this joint pattern is pretty unusual," the archaeologist said at length.
"It's far from being unknown," Lampert replied. "I got my first large taste of it in my student days back on Earth. Fly over the mesa country in southwestern North America sometime. Most of the joints there are invisible from a distance, of course; but at the edge of a butte where weathering is most prominent the blocks have frequently started to separate, and the thing looks as though it had been put together from outsize bricks."
"Hmph. Seem to remember something of the sort myself, now that you mention it. I did some digging in that area, too. I shouldn't have connected that sort of country with what we have here, though."
"Different meat; same skeleton," replied Lampert.
"But how about this volcanic ash, or mud, or whatever it is, which at least fills the joints we saw in the cliff? That's not so usual, is it?"
"Not in my experience. But granting the joints and the volcanoes, there's nothing really surprising about it. Incidentally, we don't know that this crack we're standing on has the same filling. We'd better bore down again to make sure. At least we may get some idea of the date of the volcanic action compared to that of the orogeny that tilted the block where we're camped. If there's tuff down here too, it will substantiate the idea that the vulcanism is the older."
"Why? Couldn't ash have settled down here as well as up there at substantially the same time?"
"It could. But I'd bet a fairly respectable sum that the tuff we saw in the canyon was from a mud flow, not a fall of airborne ash. That could hardly have reached the top of the cliffs—actually, the opposite slope of the mountains, where Sulewayo is working—and this area simultaneously."
"Maybe from different eruptions? I get the impression that this world has a slight tendency to produce volcanic fields rather than individual cones or flows."
"Might be. Chemistry will probably settle that question." During the latter part of this discussion Lampert had directed the mole once more downwards, and every half meter of travel another core was added to the collection. At six and a half meters below the soil the first solid specimen arrived; the others had been held together only by roots. This one, however, caused the two scientists to look at each other. Lampert nodded slowly, with a smile. Mitsuitei gave a shrug, and let an expression of resignation play over his usually impassive features.
The core was tuff, apparently identical with that in the cliffs to the east. It even contained fossils.
"I guess this whole dig might as well be taken over by the paleontology department," Lampert commented finally. "I suppose they'll at least want to compare fossils in the tilted and level strata."
"I suppose so." Mitsuitei was turning the little cylinder over and over in his hand. "Tell me, Rob, what's this little speck of green?"
"Copper salts of one sort or another, I suppose." Lampert was not greatly interested. "A lot of secondary minerals form in and under volcanic detritus. On this world, carbonates like malachite should form quite readily."
"Why should it form in a regular thread like this?"
"You mean a vein? Hard to tell precisely. Varying rates of water seepage, varying degrees of oxygen or carbon dioxide penetration, varying degrees of compactness in the rock where the stuff is formed—"
"I don't mean a vein. This is in a cylindrical body going right through the core from one side to the other, as though there had been a copper wire there originally which had been attacked by soil acids."
"Let's see. You're right. It's hardly an ordinary vein, though your suggestion seems a trifle far fetched. The paleontologists can probably furnish an idea. Maybe a vine or even a worm buried in the mud flow acted as the precipitating agent for copper salts in the subsequent seepage—I've seen beautiful fossils of pyrite which had been formed that way."
"But this shows no trace of structure, except for its exterior shape."
"Isn't a really well preserved structure the exception rather than the rule in fossils?"
"I suppose so. Still, I'd like to know just how far, and which way, this green thread goes. I'd also like to know whether there are dilute copper deposits spread through this rock, which could be concentrated in the way you suggest."
"The first could be learned by taking enough cores. The other would call for some very careful analysis of samples which had been selected with a very sedulous eye kept on the stratigraphy. You know that; you must have done that sort of thing looking for carbon-fourteen samples, at times."
"Yes, I see that. Could you make such analyses here?"
"No, except for the mere presence of copper. The cores would have to go back to a well equipped lab. Still, if you want to get them, it's all right with me. Problems were made to be solved. I'll admit this one doesn't seem very exciting to me, but I can use your data after you finish for work of my own. You should wind up with material for a pretty complete geochemical picture of this neighborhood. Shall I get the cores for you?"
"Yes, please."
"Silly question. All right." The mole was drawn up a short distance, and sent questing downward once more at an angle to the original shaft, branching off a short distance above the level from which the copper deposit had come. Again and again the process was repeated, each time at a slightly different bearing from the central hole; and Mitsuitei examined each core for traces of green. At last he found it, piercing the little cylinder of rock as the other had done; and then, at his suggestion, Lampert reset the mole to get a sample in the opposite direction from the one which had furnished the new specimen.
This also checked positive; and four more samples, taken along the same line at various distances, all did the same.
Apparently the line of green extended for some distance, about parallel both to the surface of the ground and the trend of the joint in which it was buried. Mitsuitei was radiant.
"I'm going down to that level if I have to come back with an expedition of my own! If that's a fossil worm, it's worth getting the whole length anyway—but I don't believe it is. I—"
"That will take a lot of time, you know," Lampert pointed out mildly.
"Certainly I know! Even if I use your fast excavator down to the tuff level, I'll have to do detail work from then on. What of it?"
"Well, the others may have jobs they want to do—"
"Then they can do them! What are we here for, anyway? I thought it was to investigate the past of this planet! Ndomi and Hans are doing that their own way right now. Why can't I? I'm an archaeologist, and I came along to do any archaeological work that presented itself to do; this is the only thing of the sort anyone's seen so far. I know what you're thinking. Maybe you're partly right. I certainly won't bet any money that this thread of green is a fossil telephone wire; but it's as likely to be that as anything else you've suggested, and I'm going down to that level and sift the whole volume. Hans and Ndomi can have any fossils I find if that will make you happier—and if one of them says he has no use for fossils he didn't dig himself, I'll make him eat his words. I can identify, locate and report on anything that turns up in a rock as well as any of those jigsaw-puzzle people; and I can do it in mud, too, which is more than any of them could manage."
"Don't get hot under the collar. If you can help it on this planet. You sound as though one of the boys had been giving you a lecture on the importance of knowing what strata a given series of specimens represent."
"Not one of our boys—they have a little more sense. But there was a young paleontologist when I was covering the Antares worlds whose memory still makes my blood pressure go up. Never mind me; that's not important. But I want to make this dig."
"It will tie up machines, however freely we can spare time," Lampert said slowly. "I'll tell you: how about this? W............