They swam back into the tunnel, dressed, and went out.
"We have come out, Maria," Bertie called. "The coast is clear for you. The water is not so deep as we thought it was, and you can walk out to the point where the roof comes down on to the water without getting out of your depth."
It did not take them long to cut a number of switches to serve as brooms, and a couple of handles. They carried them up into the house, and lashed the switches firmly on to the handles. The work was rough, but the brooms when completed were large, and, although not strong enough for heavy work, would do well to sweep aside the thin layer of almost impalpable dust on the floor below.
"No; I think a fire would be a drawback rather than an assistance. It would be very valuable if we were working at one spot, but it could give no general light in a place a hundred feet long. We will take a torch down, and hold it and sweep by turns. We shall only want, to begin with, to make a clear path a couple of feet wide down the middle. Of course later on we shall clear it all. That will be sufficient to enable us to see how the floor is constructed, whether with big blocks or small ones, how closely they are fitted together, and so on. It is certainly unlikely that we shall find any indication as to where chambers exist."
It took but a very short time to clear the path; the dust was so light that one sweep of the broom cleared it away. When they got to the farther end they returned to examine the floor. For four or five feet from the cistern the rock had been evidently untouched, except to cut off any projecting points. Then there was a clear line running across the path. Bertie held the torch down close to it. Harry knelt down and examined it.
"This is a clean cut, Bertie. It is evidently solid above this, but the stone is not quite the same colour on each side of it, and it looks as if they had cut away the rock here and begun to build so as to keep the floor level. The cut may be six inches deep and it may be a foot, that doesn't matter. The face of this stone is very smooth, but it is not cut; it is, I think, the face of the natural fracture. Move the torch along and let us see where the next join is. Ah, here it is!"