Out of this he crawled, only to discover himself thus landed in a great and perfectly circular plain of about thirty acres in extent, or about three hundred and fifty yards in diameter.

In the center was a lake, also circular.

The broad belt of shore around this lake was covered with rich grass, level as a bowling green, and all this again was surrounded by a nearly perpendicular cliff, down which indeed he had fallen.

This cliff was thickly clothed with shrubs and trees.
Hazel recognized the crater of an extinct volcano.
On examining the lake he found the waters impregnated with volcanic products.

Its bottom was formed of asphaltum.