For example, JJA Worsaae used this law to prove the Three Age System.

Cross-dating of sites, comparing geologic strata at one site with another location and extrapolating the relative ages in that manner, is still an important dating strategy used today, primarily when sites are far too old for absolute dates to have much meaning.It was now possible to assign a calendar date to archaeological sites in the American southwest for over 1000 years.Determining calendar rates using dendrochronology is a matter of matching known patterns of light and dark rings to those recorded by Douglass and his successors.Seriation, on the other hand, was a stroke of genius.

First used, and likely invented by archaeologist Sir William Flinders-Petrie in 1899, seriation (or sequence dating) is based on the idea that artifacts change over time.Dendrochronology has been extended in the American southwest to 322 BC, by adding increasingly older archaeological samples to the record.