We used GPR this summer on an unplowed Spanish mission site c. 1741-1761
here in Florida (with a short-lived Spanish cavalry outpost as well), where
we had already excavated sections of several wall trench structures,
including a very substantial post-on-sill wall trench with many in-place
forged nails.  Despite the fact that excavations have subsequently confirmed
that this undisturbed trench runs more than 12 meters across the prior GPR
survey area, cutting through the alluvial clay terrace soils below, there
was no apparent GPR signature of that structure (nor, for that matter, any
corresponding signature in the soil resistivity survey).  We did, however,
find a substantial "cloud" of metal-detector hits in general association
with this structure (which we suspect was the cavalry barracks built in
1760), and with the site in general as compared to surrounding areas.  There
were too many hits to define wall outlines from the ground surface, but on a
much smaller scale we were indeed able to trace the trench from one meter to
the next using nails spaced at 8-9 inch intervals within the trench, moving
from the known to the unknown.

I know of at least two other examples of metal detector surveys working
quite well to define the locations of mission structures here in Florida (in
those cases dating to the early 17th century), both in woods and pastures,
and our results would seem to confirm that strategy as the most likely to
generate good results.

John Worth

On Mon, Sep 13, 2010 at 8:35 PM, Benjamin Carter <
[log in to unmask]> wrote:

>  All,
>
> I am in the process of studying a historic site (c. 1750) in eastern PA.
> Based upon historic documents we have a good idea of the location of the
> site and part of it falls within an open field. I have been over the site
> multiple times and there are very few hints as to where within that field
> the site may be. There may have been one structure that had a stone
> foundation, but that may have been removed historically. There were probably
> approximately 35-50 other 'houses' that did not have stone foundations. I
> want to try an relocate these structures based upon their post-holes,
> trenches and artifacts, especially nails. At least one of the structures was
> burned so the nails should be distributed around that foundation. These has
> been some historic disturbance at the site, but I don't believe that
> structures were buried, but they were likely plowed.
>
> I am trying to figure out the best way to relocate the site more precisely.
> I would love to use either GPR or Magnetometry, but the equipment can be
> extremely pricey and I have a fairly limited budget. There are also a myriad
> of variations that I could potentially use and I am having a difficult time
> determining which would be the best.
>
> Does anyone have suggestions? Are there inexpensive GPR, etc. equipment
> that I could rent? I am considering using metal detectors in the organized
> fashion laid out in previous posts to this list serve.  That seems more
> affordable and I may know a couple of people who have them and, hopefully,
> would help out. Unfortunately, that doesn't give me a great map like you can
> get from GPR. It is also limited because it gives little information about
> the item that has been detected.
>
> I greatly appreciate any and all assistance.
>
> Cheers,
> Ben Carter
>



-- 
John E. Worth, Ph.D.
Assistant Professor, Department of Anthropology
University of West Florida, 11000 University Parkway, Pensacola, FL 32514
Phone: (850) 857-6204    Fax: (850) 857-6278
Email: [log in to unmask]
Home Page: http://www.uwf.edu/jworth/
2009-2010 Field School Blog:
http://pensacolacolonialfrontiers.blogspot.com/