|This photo is taken along the Macomb access ramp
to Route 60, heading east. The top of the white post marks a narrow
band of Northview Shale.
Shale is a sedimentary rock composed of very small to silt-sized
particles of clay. Shale results from the deposition and compaction of
fine-grained material (mud) on the bottom of a quiet sea floor. Relatively
minor amounts of shale occur within most of the carbonate rock formations
as thin layers and lenses. However, in the northernmost part of the Bryant
watershed is a shale layer that is ten to twenty feet thick or more. This
is a layer called the Northview Shale, which is Mississippian in
age and occurs between the Compton and Pierson limestones.
|A closer view of the shale shows that it is made
up of thin layers. The band is between 6 and 10 inches deep.
Shale is by nature a relatively soft rock that is easily
eroded and seldom seen in a natural outcrop. Northview Shale is exposed
in a roadcut along Highway 60 in southwestern Wright County. At this location
the shale is a grey to greenish grey crumbly rock that is deeply eroded
along the roadside. The shale contains numerous thin veins or fracture
fillings of brown iron oxide (limonite). In some localities the shale
contains numerous fossils that have been replaced by the limonite.