The slab was four feet across.
"You had better sweep the dust off both ways, Bertie, so that we may see what size it is."
It was, they found, about eight feet long.
"It has straight edges, Harry, almost as straight as if it had been sawn."
"Very likely it was sawn, Bertie; They could have had no tools that would cut a hard stone like this regularly, but as they were certainly clever builders they must have employed some means to do it. Possibly they used a saw without teeth, for however much they might have hardened the copper, the teeth could not have stood, but if they had a hard copper band fixed like the saw some masons use, and kept the stone moistened with fine sand, they might have cut into it. Of course it would have been a slow process; but they would not have needed to go far into the stone, for when they got down two or three inches they might have broken it through by dropping a heavy weight on the end. It would not have mattered if the fracture had not been straight below the cut, for only on the surface would they have wanted to fit accurately to the next stone. In another way they might have got a straight edge, that is, by driving very dry wedges into the cut made by the saw, and then moistening them. I know that great stones can be split in that way. They may have used both methods. However, it doesn't matter to us much how they did it. It is clear that they could in some way or other cut stones. As they took the trouble to do so here, we may conclude that they were anxious to have a smooth floor that would be extremely difficult to get up.
"They would never have taken all this trouble if they had merely been making a floor for a cellar. For that purpose it would only have been necessary to throw rocks and stones of all sizes into the vacant space below, and when it was nearly full, to level it with small stones and sand. That they chose to undertake such tremendous labour as the making of so regular a floor as this must have been, shows that they had some very strong motive for doing so."
Going carefully along the track they had cleared, they found that the stones were of different sizes; some were but two feet wide, others as much as ten, but all fitted so closely together that it was difficult to see the joints.
"It is going to be a hard job to get these out, Bertie," Harry said, when they had completed their examination, "and it is lucky for us that the room gradually narrows from sixteen feet wide to two at the other end, and when we stepped it we made it eighty feet long. We need not take up the stones near the rock wall, for the ravine would naturally narrow as it went lower, and the depth would be greatest by the side of the wall of the tunnel."
"Well, we shall soon blow up the stones when we have got the powder."
"I hope so, Bertie; but I see that we shall have difficulty unless these top stones are extraordinarily thick."