Page:Popular Science Monthly Volume 1.djvu/281

Rh continue indefinitely around the margins. Thus, in many places, the tops of adjacent trunks have joined together, forming a coral floor resting upon arches and pillars built without axe or sound of hammer. In some parts of the reef-region, such united coral-heads cover large areas. A magnificent scene would be presented should the waters recede and leave bare these arches and columns. The ruins which "sentinel the desert" would not rival them in grandeur. To thread their avenues and sounding aisles would be the labor of a lifetime.

The illustration, Fig. 12, after a sketch by Prof. C. F. Hartt, in his "Geology of Brazil," is of an area of the sea off that coast, abounding in coral-heads similar to those described. "The corals," says Prof. Hartt, "grow in the open sea, and often rise 40 or 50 feet, and form what the natives call chapeiroes (signifying 'big hats').



They are abundant on one part of the coast over an area of 40 square miles. A vessel running on the top of one of these chapeiroes would remain perched like a weathercock on the top of a tower, to the great amazement of the captain who finds deep water all around." Inside the outer or barrier reef the water is smooth as in an inland bay. If free from sediment, and not freshened by discharge from rivers, it is the paradise of the smaller corals. The beautiful fungia lie with innumerable shells upon the bottom. The feathery and fan corals grow in clusters, and, amid their delicate plumes, fishes, which rival them in gayety, [sic] glide through the transparent water.

It is a peculiarity of coral-reefs that the outer side is usually nearly perpendicular, while the inner side is a gentle declivity. The cause of this may be better understood if we follow the development of the reef from its beginning. Upon a shore of sand or rock, and at a depth of less than 120 feet, the reef-builders attach themselves