Unfortunately, the wood from the pueblos did not fit into Douglass's record, and over the next 12 years, they searched in vain for a connecting ring pattern, building a second prehistoric sequence of 585 years.
In 1929, they found a charred log near Show Low, Arizona, that connected the two patterns.
Seriation, on the other hand, was a stroke of genius.
Like tail fins on a Cadillac, artifact styles and characteristics change over time, coming into fashion, then fading in popularity. The standard graphical result of seriation is a series of "battleship curves," which are horizontal bars representing percentages plotted on a vertical axis.
Plotting several curves can allow the archaeologist to develop a relative chronology for an entire site or group of sites.
Douglass believed that solar flares affected climate, and hence the amount of growth a tree might gain in a given year.
His research culminated in proving that tree ring width varies with annual rainfall.
For example, JJA Worsaae used this law to prove the Three Age System.
For more information on stratigraphy and how it is used in archaeology, see the Stratigraphy glossary entry.
For detailed information about how seriation works, see Seriation: A Step by Step Description.
Seriation is thought to be the first application of statistics in archaeology. The most famous seriation study was probably Deetz and Dethlefsen's study Death's Head, Cherub, Urn and Willow, on changing styles on gravestones in New England cemeteries.
The main drawback to dendrochronology is its reliance on the existence of relatively long-lived vegetation with annual growth rings.
Secondly, annual rainfall is a regional climatic event, and so tree ring dates for the southwest are of no use in other regions of the world.
Many of the first efforts of archaeology grew out of historical documents--for example, Schliemann looked for Homer's Troy, and Layard went after the Biblical Ninevah--and within the context of a particular site, an object clearly associated with the site and stamped with a date or other identifying clue was perfectly useful. Outside of the context of a single site or society, a coin's date is useless.