_Ricker Mills_
Just south of the park at Ricker Mills some of the oldest rocks in the
area are exposed in the railroad cut just north of the highway crossing.
These rocks belong to a thick sequence of similar rocks which are
collectively called the _Waits River formation_. Studies in other areas
indicate that these rocks belong to the portion of geologic time called
the Ordovician period which was more than 350 million years ago.
The Waits River formation represents a series of sediments which
accumulated at the bottom of a shallow sea during Ordovician time. These
sediments included both limy and sandy beds, and fossils may originally
have been preserved in some of the beds. Sediments of other types later
accumulated over the Waits River formation during a long period of
geologic time, so that eventually the formation became deeply buried.
(See Figure 3.) The sea retreated and the rocks were subjected to high
pressure and temperatures during a period of mountain-building. The
rocks which had been sedimentary were folded and converted to
_metamorphic rocks_ by partial melting and recrystallization of the
components. As a result the rocks became schists or marbles. Any fossils
which may have been present were destroyed or badly altered in the
process. This is unfortunate because valuable geologic information as
the age of the rocks can be determined from the type of fossils present.
The rocks of the Waits River formation at Ricker Mills are dominantly
mica schists with layers containing limy material. These are too impure
to be considered marble but enough lime is present so that they react
strongly with acid, a test for detecting the presence of lime. The
schists principally contain quartz, biotite, calcite (lime) with lesser
amounts of muscovite, feldspar and impurities. The rocks weather to dark
colors; the gray limy beds are particularly susceptible to weathering
and turn dark brown to black on the surface. When more lime is present,
the rock weathers to a deep brown porous rock which resembles decayed
wood. Some boulders of these altered limestones are found in the glacial
deposits in the State Forest.
An additional factor which makes the rocks in the railroad cut at Ricker
Mills look “messy” is the iron and manganese staining and the formation
of mineral crusts on the surface of the rocks through the action of
ground water. Rain water falling on the hills above passes through the
soils, dissolving minerals, and precipitating them where the water seeps
out and evaporates at the lower level of the railroad tracks.
The schists trend about N.80°W. and dip about 30° to the northeast.
Along the length of the rock exposures it can be seen that this dip is
not constant but varies from 10 to 30°. The variation in dip gives the
schists a wavy appearance.
At two places along the railroad cut, the schist has been intruded by
granite. As is shown in Figure 6, which is a sketch of the rocks exposed
on the east side of the railroad, the granite forms vertical dikes. As
the schist ends abruptly at the contact of the granite, this indicates
that the granite formed after the schist. The granite is nearly the same
as the granite in Groton State Forest except that the mica is muscovite
rather than biotite. For this reason the granite is lighter in color on
fresh surfaces. In general the exterior is dark in color due to the
staining of iron from weathering of the mineral pyrite, an iron sulfide,
which occurs in small amounts in the granite.
_Jerry Lund Mountain_
On top of Jerry Lund Mountain occur other outcrops of the Waits River
formation and granite. Their exact relationships cannot be seen easily
because of the thick vegetation. The Waits River formation on Jerry Lund
Mountain is composed principally of quartz mica schist.