Hi ya'll.   I have a question for all those brick experts out there.  
Several years ago we put a test trench across a portion of what was once a
prison for Union Soldiers in Cahawba (Civil War vintage).  The building
started its life as a railroad & steamboat warehouse (probably primarily
for cotton storage).  Although the area beneath the wood floor was used  
for a year or two as a church for the enslaved laborers of the town and
surrounding plantations.  The structure was built just prior  to the War, 
1860-1861 out of brick.  The town had three brickyards.   All that's left 
of the structure was a line of rubble where the wall once stood.  Oddly
enough about one out of every 30 or so brick bats that we pulled out of the
trench had a large impression on it.  The impression was probably about 1/4
of an inch deep and about  4 inches long.  It was in the shape of a large 
key hole - that is,  it was a large round impression with a small
retangular appendage attached to one side.  Of the bricks that had this
impression, each impression was identical in size and shape.  My question 
is: do any  of you know what this mark was and why did we find it only on a
small percentage of the bricks?   I'd appreicate any suggestions.  Thanks 
in advance.
Linda Derry
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