The geologic time scale: USGS holds firm

Just as the United States holds onto the foot-mile system and the Fahrenheit temperature scale, the U.S. Geological Survey has long maintained an independent system of geologic time and map colors. Tradition—that is, continuity and stability—is a good reason, but the rocks matter too. The gross Cenozoic stratigraphy of the continental USA lends itself to a division into Tertiary and Quaternary rocks; also the palette of American rocks makes for an ugly map if it's based on the European color standard. So while the International Stratigraphic Commission has, for the moment, erased the Tertiary and Quaternary, the USGS retains them in its new time standard, issued in March. See the two versions of the Cenozoic, including the respective colors, together on one page. And although the ISC has recently given the name Furongian to the Upper Cambrian Period, the USGS will wait until all three periods of the Cambrian have new names before changing from Lower, Middle and Upper. In all other respects, the world and the USGS are on the same page. In fact, the USGS now acquiesces to having national-scale US geologic maps follow the international colors.