What's see in the James River basin in VA are rows of about 4" deep, 4"
apart holes of about 0.5-0.75" diameter, all with rounded bottoms. The
rocks are split using the feather and wedge system. Suitable numbers of
failed splits are extant to show the sequence. This appears on 19th
century specimens. Post-splitting dressing removes most of the holes,
however, on many structures. Later, one sees the ±1" drill holes for
explosives. One variant I've seen on an early 19th century mill using
soft sandstone blocks was a 1.5-2.0" long x 0.5" slot cut at 4-6"
intervals along the split.
As a cautionary note, some technology shifts have a 50-75 year lag
making it west. I've seen 18th century canal locks in Yorkshire which
are identical in form and stone dressing style to those of the 1830-50's
here in VA.
Lyle
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
|