Coral Island Small 320×295 Medium 640×590 Large 1024×944 Download Tiff Original 2400×2213 | (2.2 MB) Description The reef forming the island is of limestone, derived form countless skeletons of minute polyps that once lived beneath the surface of the waters. Keywords geology, ocean, sea Galleries Coral Reefs Source: Edwin J. Houston, The Elements of Physical Geography, for the use of Schools, Academies, and Colleges. (Philadelphia: Eldredge & Brother, 1891) 41