Part 2

Almost all of the boulders deposited by the glacier are composed of white granite similar to the rock which underlies the entire area. This indicates that most of the boulders have not been transported very far. However, occasionally boulders are found which are not characteristic of the area and represent rocks brought in from the north. Such boulders which are foreign to the area in which they are found are called _erratics_. Most erratics in this area are dark-colored metamorphosed rocks in which the minerals are oriented to give the rock a layered pattern. These are called either _gneisses_ or _schists_ depending on whether the layering is coarse or fine. Deposits of the glacier are exposed in two gravel or sand pits near the Stillwater Camp site. These deposits are composed principally of sand but contain scattered boulders of different sizes. A few erratics are found in these deposits—particularly a variety of rock which weathers to a soft, brown porous mass resembling decayed wood. These sandy deposits probably were plastered onto the ground from the sole of the creeping glacier or were simply let down as the glacier wasted away.

Because of the irregular manner in which the glacier may deposit its load of sand and gravel, the topography in such areas is uneven and characterized by poor drainage. At a number of places in Groton swampy areas occur at higher elevation which might normally be expected to be well-drained. Some of these areas have become the sites of beaver dams because they are ideal for damming up the water.

GEOLOGY OF NEARBY AREAS

_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.

TRIPS TO TAKE

_Hiking in the State Forest_

The hike from the end of the road to the top of Owlshead Mountain takes only ten to fifteen minutes. A splendid view of the surrounding area, particularly Groton and Kettle ponds, is obtained from here. If possible, everyone who visits the park should take this short walk. The granite is well-exposed at the summit and dikes of aplite and pegmatite may be seen.

The more venturesome park visitor will want to make other trips away from the “beaten path” into the wilderness of the Vermont woods. The principal difficulty arises in that the wilderness is so real a person may well become lost if he strays too far from the trails. Some of the trails have become overgrown so that they are difficult to follow and portions of others have been destroyed by the damming up of brooks by the beavers. It is suggested that in planning hikes information be obtained from the park superintendent about the condition of the various trails.

GRANITE WAITS RIVER FORMATION

An interesting hike can be made from Osmore Pond to Deer Mountain but as the trail is poorly marked, one must maintain a sense of direction. From the Osmore picnic area walk south near the shore of the pond to its outlet into Osmore Brook. At this point turn left to the northeast and follow the trail which parallels a wire marking the edge of the game preserve. About three-fourths of a mile from Osmore Brook the trail meets another trail at right angles. To the left the trail follows the game preserve boundary northwestward. The trail to the right leads directly to the top of Deer Mountain where a view may be obtained on the south side of the summit. As an alternate route for returning, follow the trail along the game preserve to the northwest. Some distance beyond a shelter-lean-to the trail divides several times with the main trail leading to Blake Hill and other trails to the left leading to the Osmore Pond road.

A hike along the trail on the north side of Kettle Pond to the shelter-lean-tos makes a pleasant trip along the water. Also, the trail from Owlshead Mountain to Osmore Pond is convenient for a short hike through the woods, if the trail can be found.

_Quarries at East Barre_

The granite quarries at East Barre are in nearly the same type of rock as that which occurs at Groton State Forest. The quarry operations are interesting and educational and the quarries afford a good opportunity of seeing fresh, unaltered specimens of granite. Guide service is offered at some of the quarries.

FOOTNOTES

[1]_Granite_ is a type of igneous rock consisting of large interlocking grains of light-colored minerals. Rocks are classified as being either igneous, sedimentary, or metamorphic. _Igneous_ rocks form by the solidification of molten material; _sedimentary_ rocks form by the accumulation of sediments derived from older rocks; and _metamorphic_ rocks form by the recrystallization of older rocks under conditions of high temperatures and pressures.

[2]_Dip_ is the inclination of a surface as, for example, a joint surface described above.

[3]_Schist_ is the name given to rocks in which the minerals have a parallel alignment due to reorganization of the rock constituents during a condition of high temperature and pressure. The platy minerals, like mica, form at right angles to the pressure so that the resulting rock may have a “bedded” appearance.

Transcriber’s Notes

—Silently corrected a few typos.

—Retained publication information from the printed edition: this eBook is public-domain in the country of publication.

—In the text versions only, text in italics is delimited by _underscores_.