Carol Serr

Here is what I can gather from your posting asking about the dates of the
I-Diamond marked Illinois Glass Company bottles.  It appears that you have
assumed that the arrangements for city trash pickup in 1914 are probably
the terminal event for the dump area that you monitored.  You appear to
have taken what might have been the terminal event and chosen to call it
the Terminus post quem.  In reality, your trash pickup ordnance should be
termed a Terminus ante quem.  To put it another way, you expected all of
the artifacts from this deposit to date before the 1914 change in garbage
pickup.  The TPQ artifact is the most recently made object in any context.
By logic, anything found with or above the TPQ artifacts has to have been
deposited after the date of its production.  I have seen some people refer
to the "TPQ" artifact for a site, which is silly, especially for sites with
long occupations.  We use the TPQ artifacts from deposits to date the
layers above as having to be deposited after the TPQ date of the objects
below them.

      You mentioned that you have a mean date of 1907 from over 250
artifacts.  Are you mixing glass, ceramics and other artifacts together for
this mean date?  Glass was becoming a disposable artifact with a short use
life by the early twentieth century, where as things like ceramics had much
longer use-life spans and thus the mean dates on ceramics will be earlier
that that of your glass.  See Bill Adams article on Time-Lag in the latest
issue of Historical Archaeology.


George L. Miller
URS Corporation