Pozzuoli's Pillars Revisited

Natural History, May, 1999 by Stephen Jay Gould

In his long-delayed 1847 publication, Babbage added an appendix to describe the recent subsidence also noted by Lyell in later editions of his Principles of Geology. Babbage discussed the observations of Niccolini and Smith as reported to the Geological Society of London: "Mr. Smith found the floor of the temple dry at high water in 1819, and 18 inches on it at high water in 1845." To reach his general uniformitarian conclusions, Babbage then integrated these latest data with his previous observations on earlier changes in historical times:

   The joint action of certain existing and admitted causes must necessarily
   produce on the earth's surface a continual but usually slow change in the
   relative levels of the land and water. Large tracts of its surface must be
   slowly subsiding through the ages, whilst other portions must be rising
   irregularly at various rates.

To generalize this Neapolitan conclusion, Babbage then cited the ongoing work of a young naturalist, based on entirely different phenomena from the other side of the globe: the coral atolls of the tropical Pacific Ocean. This young man had not yet become the Charles Darwin we revere today (publication of the Origin of Species still lay twelve years in the future, and Darwin had revealed his evolutionary suspicions to only a few close confidants, not including Babbage). Therefore, Babbage and the scientific community of Britain knew Charles Darwin only as a promising naturalist who had undertaken a five-year voyage around the world; who had published a charming book on his adventures and three, more technical volumes on the geology of South America and the formation of coral atolls; and who now stood in the midst of a comprehensive treatise, which would eventually run to four volumes, on the taxonomy of barnacles.

Of this interesting work, Darwin's theory on the origin of coral atolls surely struck colleagues as his most important and original contribution. Darwin, labeling his explanation as the subsidence theory of coral reefs, explained the circular form of atolls as a consequence of subsidence on the surrounding sea floor. Reefs begin by growing around the periphery of oceanic islands. If the islands then subside slowly, the corals can continue to grow upward, eventually forming a ring as the central island finally disappears below the waves.

This brilliant--and largely correct--explanation included two implications most favorable to Lyell and his fellow uniformitarians, hence their warm embrace for this younger colleague. First, the subsidence theory provided an excellent illustration for the efficacy and continuity of gradual change--for corals could not maintain their upward growth unless the central islands sank slowly. (Reef corals, filled with symbiotic photosynthetic algae, cannot live below the level of penetration by sunlight into oceanic waters, so any rapid subsidence would extinguish the living reefs.)

Second--and more crucial to the work of Babbage and Lyell at Pozzuoli--the large geographic extent of atolls proves that major regions of the earth's crust must be subsiding, thus also implying that other regions of comparable extent must be rising at the same time. Therefore, the fluctuations recorded on Pozzuoli's pillars do not only represent a local phenomenon but also illustrate one of the most fundamental principles of the gradualist, nondirectionalist, and uniformitarian mechanics of basic planetary behavior.