We learn from Lieutenant Nelson, that, in the Bermuda Islands, there are several basins or lagoons almost surrounded and enclosed by reefs of coral. At the bottom of these lagoons a soft white calcareous mud is formed by the decomposition of _Eschara_, _Flustra_, _Cellepora_, and other corallines. This mud, when dried, is undistinguishable from common white earthy chalk; and some portions of it, presented to the Museum of the Geological Society of London, might, after full examination, be mistaken for ancient chalk, but for the labels attached to them. About the same time Mr. C. Darwin observed similar facts in the coral islands of the Pacific; and came also to the opinion, that much of the soft white mud found at the bottom of the sea near coral reefs has passed through the bodies of worms, by which the stony masses of coral are everywhere bored; and other portions through the intestines of fishes; for certain gregarious fishes of the genus _Sparus_ are visible through the clear water, browsing quietly, in great numbers, on living corals, like grazing herds of graminivorous quadrupeds. On opening their bodies, Mr. Darwin found their intestines filled with impure chalk. This circumstance is the more in point, when we recollect how the fossilist was formerly puzzled by meeting, in chalk, with certain bodies, called cones of the larch, which were afterwards recognized by Dr. Buckland to be the excrement of fish.[216-A] These spiral coprolites (see figures), like the scales and bones of fossil fish in the chalk, are composed chiefly of phosphate of lime. [2 Illustrations: Fig. 217. Fig. 218. Coprolites of fish called _Iulo-eido-copri_, from the chalk.] Mr. Dana, when describing the elevated coral reef of Oahu, in the Sandwich Islands, says, that some varieties of the rock consist of aggregated shells, imbedded in a compact calcareous base as firm in texture as any secondary limestone; while others are like chalk, having its colour, its earthy fracture, its soft homogeneous texture, and being an equally good writing material. The same author describes, in many growing coral reefs, a similar formation of modern chalk, undistinguishable from the ancient.[216-B] The extension over a wide submarine area of the calcareous matrix of the chalk, as well as of the imbedded fossils, would take place the more readily, in consequence of the low specific gravity of the shells of mollusca and zoophytes, when compared with ordinary sand and mineral matter. The mud also derived from their decomposition would be much lighter than argillaceous and other inorganic mud, and very easily transported by currents, especially in salt water.