. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. 108 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. probably consisting of aragonite. It will be noticed that the " mud " lining the coral walls has crystallized in prismatic needles of aragonite deposited in optical continuity with the fibers of the coral. The above description represents the appearances of the less altered reef-forming corals. The more commonly occurring constituents of the limestones are, however, compacted " coral sand," detrital fragments of organisms, and a certain amount
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. 108 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. probably consisting of aragonite. It will be noticed that the " mud " lining the coral walls has crystallized in prismatic needles of aragonite deposited in optical continuity with the fibers of the coral. The above description represents the appearances of the less altered reef-forming corals. The more commonly occurring constituents of the limestones are, however, compacted " coral sand," detrital fragments of organisms, and a certain amount of rubble rock. A section of a com- pacted " coral sand " is composed of organic fragments from the Fig. 3. Christmas Island, No. 372. (After boiling with cobalt nitrate.) The arago- nite organisms, corals, gastropods, and Halimeda, as well as the aragonite crystals in the coral cavities, are stained pink. The calcite organisms, Orbitolites, echinid spines, and Lithothamnion, together with the fibrous calcite cement, are quite un- stained. X 30. As a rule, it shows aragonitic organisms such as coral fragments, Hali- meda, gastropods, etc., together with organisms having calcite skeletons, such as most of the Foraminifera, echinid spines, Lithothamnion, etc. The organisms are often fragmentary, and are cemented together by a matrix consisting either of " mud " or of calcite. The calcite may exist in two forms. The more usual is a somewhat clear granular mosaic of crystals, but frequently it coats the organisms with an investing layer of long fibrous crystals. A good example of the latter is seen in Figure. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Harvard University. Museum of Comparative Zoology. Cambridge, Mass. : The Museum
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