Page:Popular Science Monthly Volume 22.djvu/251

Rh in a "gravelly" beach, where a boat may be drawn up. It is 50 feet high, 48 feet broad, and 224 feet long. It is excavated in the lower stratum. Thus two tunnels of the same dimensions are supposed to have been driven into two different materials by the same force. The interior dimensions are nearly the same to the end. As no sentimental or religious motive can be assigned to Nature for this freak, it is amenable to comparison. The Blue Grotto of Capri is typical. Its entrance is scarcely three feet in height; in the interior the roof rises to a height of 41 feet; the water is 8 fathoms deep; length of the grotto,



175 feet; greatest width, 100 feet. Here the great size of the aperture is further increased. The superior part of the front, penetrating into the columnar basalt, has hollowed a recess above the main opening. The same Gothic tympanum, distorted by the material, not only marks its artificial origin, but disproves the allegation that the columns could not form a natural architrave. The Boat Cave is accessible only by sea. It is a long opening, resembling the gallery of a