While they were at work Alfred was lying with his back against a low mound. He happened to turn around and noticed that the upper part of the elevation was smooth, and contained certain marks and inscriptions. "What's this?" shouted Alfred, as he arose and gazed down on it. Ralph, somewhat startled, sprang out of the hollow and drew himself up. "What have you got?" he asked. "Here is a mark of some kind; now what can it be?" said Alfred, pointing down to the stone. "That is singular," remarked Ralph. "A cross, a circle, two arrows, and a set of figures. I suppose it means something, and is there for some purpose." [Illustration: _A German Range-finder_] "It may be a surveyor's post; no, that's not the name of it either. What was it the professor called the marking place where they measure from?" asked Alfred. "I don't know what you mean," said Ralph. "Why, when they locate a station, or a particular spot and then sight from that place to the next;—what is it called?—oh, I know; it's a _bench_," said Alfred. "So it is; I had forgotten the name," answered Ralph. Frisky kept on digging, and had worked his way in until he was almost hidden. "I am afraid you will have to stop," said Alfred, but Frisky didn't cease his efforts. "Come on, we might as well reach the top," continued Alfred, walking away. Ralph gave another glance at the inscription, and turned to follow. As he gazed across the brow of the hill he stopped. "Alfred," he said, "this arrow points straight to that hill in the southwest; do you see that figure there? I wonder if there is anything in that?" said Ralph. "I wish I had a straight stick, and then we could tell exactly," remarked Alfred, as he looked around for something to verify the assertion. "Use a string," said Ralph. "Here is one; wait, and let me stand right over the stone. Now, I'm going to stretch it and hold it parallel with the arrow below. When I give the word sight along the string and see whether or not it crosses the hill in the distance." "All right," answered Alfred. "Lower the right hand a little; it over-shoots the hill too much; are you ready?" "Yes; how is it?" asked Ralph. "Oh, it points down to the hollow left of the hill," said Alfred, "so I suppose the mark must be intended for something else." "Come on, Frisky; enough of that," shouted Alfred. "Up the hill," and he marched off whistling. After Ralph started Frisky jumped out of the hole, gave a few discouraging barks, and leaped after the boys. Within fifteen minutes the motor camp was reached; then great cave-like holes were noticed, stored with huge shells, and numerous smaller caves, in which were men lying about. "There the guns are," said Alfred. "Well, they have them nicely hidden, and I don't see how the flyers would ever pick them out the way they are arranged." A guard blocked the way, and a corporal approached. "Your business," he said.