"Having traversed the main tunnel for a distance of upward of eight hundred feet, and carefully avoiding its branches, we finally came to the object of our search. This tree, four feet in diameter, of opalized wood, stands upright on the left side of the tunnel. The lava had burned off the bark and partly carbonized the outside part, and then the whole had subsequently taken the form of opal silica. There is a space of about four inches between the tree and the surrounding lava. "By raising the candles above our heads we could look up the body of the tree some thirty feet. When we had broken off some choice specimens from the body of the tree with the hammer we left this subterranean world. On emerging from the tunnel the guide said: 'Thank God, we again see the sunlight.' "To which I replied: 'Amen.'" CHAPTER XIX STRANGE ROCK FORMATIONS--GIBRALTAR A huge projecting limestone rock, in form like a reclining lion, guards the entrance to the narrow water passage which separates Europe from Africa. This wonderful feature, the Rock of Gibraltar, extends directly southward from the mainland of Spain with which it is connected by a low, sandy isthmus. It is about three miles in length and in breadth varies from one-fourth to three-fourths of a mile. Two depressions divide it into three summits, the highest of which is about fourteen hundred feet. Let us visit the small city lying at its western base and then carefully examine this leviathan sentinel that seems to stand guard over the narrow strait. The special permission of the military commander to examine it or even to remain in the city must first be obtained; we are especially warned that cameras are forbidden and all negatives will be confiscated. The north face we find to have an almost perpendicular height of twelve hundred feet; its east and west sides also display tremendous precipices. The south face is much lower and slopes toward the sea. Fortifications of massive walls and the best of modern guns protect the lower parts and also the seaward side of the city. But what are those holes high up on the faces of the rock? They are portholes cut through the rock from interior chambers out of which cannon can be thrust and discharged at an invading enemy. We are curious to learn more about this interesting place, and on questioning our guide are told many remarkable stories.