Seriation of the design styles on the potsherds will result in a series of developments in style which are probably in chronological order. Broad straight line designs may give way to mixed broad and narrow straight lines, then to narrow straight lines, then to narrow wavy lines. The archaeologist could then maintain that sites which have potsherds with broad straight lines are separate in time from those with sherds having narrow wavy lines. He won’t know which is the older, because the sequence could work either way. Stratigraphy or the cultural similarity between other artifacts at the sites will probably resolve this problem. The reader will now have realized that many of the clocks used by archaeologists are interrelated. Relative dating clocks such as stratigraphy, pollen dating and geologic-climatic dating are utilized together where possible, and all are dependent upon the principle of stratigraphy. Crossdating is thus of vital importance and is constantly undertaken. The archaeologist tries to employ both absolute and relative clocks to find out the age of a site. Stratigraphy yields a series of relative dates for artifacts within the site; geologic-climatic and pollen dating yield a series of dates for types of sediment and samples collected in association with those artifacts; tree ring dates yield the absolute age of the site which allows the pollen, stratigraphic and geologic-climatic dates to be comprehended in terms of absolute age. Radiocarbon dates act as a check on the tree ring dates and, if they agree, lend support to the pollen and geologic-climatic dates. The pollen and geologic-climatic dates from the site are compared with similar dates from other sites as additional checks. Since the clocks used by the archaeologist tick at different rates of speed, and since not all of them are dating the same thing, the archaeologist usually ends with a series of dates for any given site. New geochronological techniques are always being invented and perfected. Here is a list of some that are expected to become available in the next few years: 1. The _obsidian hydration_ method. Obsidian, a naturally formed glass, is so constituted chemically that it takes chemicals from its environment at a slow rate. As it does so, the outside layer changes from transparent to translucent or opaque. The depth of the opaque layer, it is hoped, can be used as a measure of the amount of time since the surface was exposed. As many artifacts were made by chipping obsidian to form a sharp edge, this method may reveal the time since an obsidian artifact was made.