Lay Dam outcrop lies west of the Coosa river,
along Alabama Route 55. It is approximately 170
meters long and 10 meters high. The phyllite
matrix contains many different types of clasts
that have been deformed due to shear stress.
Bedding surfaces can be distinguished because of
differences in compostition of layers, however,
foliation is the dominant planar feature seen on
the outcrop. The orientation of the foliation is
very close to the orientation of the bedding in
the area surveyed. This lead the class to the
conclusion that the area surveyed was on a limb
of the fold.
The outcrop was originally a diamictite that
underwent metamorphism, transforming it to a
phyllite. Intense shearing was inflicted upon the
area, and now the outcrop is a mylonitic
Both brittle and ductile deformations are evident
on the outcrop. The east side of the rock holds a
small fault, with 1 mm of displacement. Shearing
is also seen. These different types of
deformation indicate the rock has been distorted
at different times under different conditions. It
is unlikely that one period of contortion would
produce small faults (brittle deformation) and
foliation and shearing (ductile deformation).
Hypotheses must be made about the physical
processes responsible for the transport of the
rocks to determine the original rock source for
the outcrop. Poorly sorted, angular, deformed
clasts in a variety of sizes were observed in the
outcrop, held in a matrix that was originally
clay. Debris flow is theorized as the transport
mechanism, possibly from mudslides.
Alternatively, glaciers may have been responsible
for the dropstones, by way of meltwater.
Juan points out a sheared inclusion
in the outcrop. The blue arrows point out