Then it disappeared altogether, and there was another flat surface of gravel and sand.
Between himself and the illuminated space on which he gazed--his breath quick and his eyes widely distended--there seemed to be nothing at all.
To all appearances he was looking into a cylindrical hole a few feet deep.

Everything between the bottom of this hole and himself was invisible; the light had made intervening substances transparent, and had deprived them of color and outlines.

It was as though he looked through air.
Then his eyes fell upon the sides of this cylindrical opening, and these, illuminated, but not otherwise acted upon by the volume of Artesian rays, showed, in all their true colors and forms, everything which went to make up the sides of the bright cavity into which he looked.

He saw the various strata of clay, sand, gravel, exactly as he would have seen them in a circular hole cut accurately and smoothly into the earth.

No stone or lump protruded from the side of this apparent excavation, the inner surface of which was as smooth as if it had been cut down with a sharp instrument.
Clewe was frightened.