Field geology has traditionally plied its science with little more than a hammer, chisel, and often a hand-lens. The geologist depicted in the main image is scrutinizing the rock with the same intensity geologists have always used, and he is about to strike it to determine its hardness and examine its inner structure. Using collected rocks, themselves diagnostic of the formations from which they were chiseled and gathered, precise location information, and a variety of theories, geologists identify the basic structures of the surface and interior of the earth and the forces and mechanisms responsible for their formation and evolution. Two smaller images complement this icon. One repeats the hammer depicted in the main image. The other shows a fossilized trilobite, an ancient crustacean that lived in the early oceans of the earth but is now extinct. The locations of these and many more fossils were used to date meticulously the various formations and their extent, and to compile the basic chronology of the earth. As with astronomy, these simple tools and procedures were still used at the time the Academy's dome was designed, but were in transition. Geology, too, was adopting the instruments and methods of physics to great advantage, and allied disciplines known as geophysics and geochemistry were developing. Still, even today, the hammer and chisel are ubiquitous tools, and examinations of fossils within strata a continuing research activity.