If the visitor confines his wanderings to the State Park the most
conspicuous geological features, or clues to the Park’s past history,
are concentrated in the clay banks and adjacent beach which border Lake
Champlain (see Fig. 4). The clays which cover the entire Park record
thousands of years of rather recent events, _geologically speaking_[5],
which took place in the Champlain Valley. These clays also record a very
significant phase in the development of present Lake Champlain. Before
discussing the clays it will be necessary to outline some of the
geological events which preceded the deposition of the clays, that is,
some of those events which took place as the last glacial ice lobe
slowly retreated up the Champlain Valley and into Canada. The author has
borrowed heavily from an article by Donald H. Chapman entitled
“Late-Glacial and Post-glacial History of the Champlain Valley” which
was published in the 1941-1942 “Report of the State Geologist on the
Mineral Industries and Geology of Vermont, twenty-third of (the)
Series.”
[Illustration: Figure 3. Water-worn concretions seen on the beach of
Button Bay State Park. The button-mold shape of some concretions led
to the incorporation of the word “Button” in the name Button Bay
(Originally, Button-Mould Bay). The chisel portion of the Alpine ice
ax head is about 5 inches long.]
During the final retreat of the last ice sheet to invade the New England
states (some 11,000 to 12,000 years ago) an ice lobe, which occupied the
Hudson-Champlain Valley, slowly wasted northward toward the Canadian
border. Melt-water derived from the melting glacial ice together with
atmospheric water (rain and snow) formed a succession of lakes dammed on
the north by the glacial ice. These lakes emptied to the south through
the Hudson Valley. This succession of lakes and intermediate lake stages
will be discussed in the following paragraphs.
[Illustration: Figure 4. View of beach, Button Bay State Park,
looking toward the southeast. The beach demonstrates several
water-level and storm-level debris lines. Note the conspicuous lack
of sand on this “clay” beach.]
The oldest lake recognized by the geologists is termed “Lake Albany” and
was confined to the Hudson Valley. At this time the area of present-day
Lake Champlain, north of the Hudson Valley, was still covered by glacial
ice which was slowly melting as the general regional climate throughout
New England became warmer and warmer. Soon the whole Hudson Valley
region began to _rise_[6] out from beneath the lake waters and “Lake
Albany” shallowed. Eventually a rock ledge emerged just south of
Schuylerville, New York (actually at Coveville, New York) over which the
waters from a new lake, Lake Vermont, began to flow.
Lake Vermont, with its rock ledge dam at Coveville, began to expand
northward as the ice front retreated up the Champlain Valley. Several
distinct stages in its development are now recognized in _features_[7]
demonstrating past lake levels which are abundantly displayed close to
Button Bay State Park. The “lake-level indicators” or features tell us,
in addition to the number of distinct lake stages in a given area,
something about past earth movements. A “line of
lake-level-_elevation_”[8] is drawn through those features outlining
each past lake or lake stage followed by a comparison of each line with
those lines constructed for older and younger lakes or lake stages. If,
for any two lake-level lines compared, these lines are not parallel, it
can be assumed that the earth’s crust was tilted during the time between
the formation of their lake-level features. This idea of tilting of the
earth’s surface, which is supported through the study of successive lake
levels, has proven the key to the present status of Lake Champlain.
At the beginning of its history Lake Vermont emptied to the south
through an outlet channel located in the vicinity of Coveville, New York
(see map, Fig. 5A). This stage in the development of Lake Vermont, often
referred to as the Coveville Stage, saw lake waters fill the Champlain
Valley from the Green Mountains on the east to a position west of the
present New York-Lake Champlain shoreline. Such Vermont towns as
Middlebury, Vergennes, Hinesburg, Burlington and Colchester would have
been submerged beneath the lake waters (see map, Fig. 5B). Certain high
areas such as Mount Philo, Pease Mountain and Cobble Hill show
lake-level features along their sides which prove that these areas were
islands rising above the level of this past lake. If you visit Mt. Philo
State Park, located approximately 11 miles north of Vergennes, one of
these lake-level features, a wave-cut terrace, can be seen at an
elevation of 545 feet and on the south side of the hill (at the level of
the second reverse turn in your trip to the _summit area_).[9]
[Illustration: _FIGURE 5_
_EARLY COVEVILLE_ _MAXIMUM COVEVILLE_]
[Illustration: Figure 6. Looking west from the top of Mount Philo
State Park. The Adirondack Mountains are on the skyline, Lake
Champlain in middle background and the Champlain Lowlands stretch
from Lake Champlain to the base of Mount Philo.]
[Illustration: _FIGURE 7_
_FORT ANN MAXIMUM_ _MARINE MAXIMUM_]
Shortly after Coveville Lake Vermont reached its maximum size (see map,
Fig. 5B), a southern gorge-outlet was formed at an elevation lower than
the previous Coveville outlet in the vicinity of Fort Ann, New York
(Fort Ann is located approximately 8 miles south of the present southern
extremity of Lake Champlain). The level of Lake Vermont’s water dropped
to the new Fort Ann Stage (see map, Fig. 7A). Evidence for this new lake
level is seen on the slopes of Mt. Philo, Snake Mountain and Cobble
Hill. These lake-level features are parallel to and found 100 feet below
those of the Coveville Stage. These parallel features, then, indicate
that very little, if any, tilting of the earth’s crust had taken place
between the Coveville and Fort Ann lake stages.
[Illustration: Figure 8. Beach and clay banks exposed along the Lake
Champlain portion of Button Bay State Park. This view is toward the
northwest and includes a major portion of the Park’s lake frontage.
Photo by Robert B. Williams.]
This Champlain ice lobe continued to melt and retreat toward the
Canadian border and beyond. As the glacial front approached the St.
Lawrence valley, fresh water from Lake Vermont began to seep through the
retreating ice lobe and into the marine waters which filled the St.
Lawrence area. Several shoreline (lake-level) features are found at
different elevations below the Fort Ann Stage of Lake Vermont and attest
to a slow lowering of the lake level by the escape of fresh water to the
north.
The conspicuous clays of Button Bay State Park were deposited during the
next episode in the history of the Champlain Valley, a development
heralded by continued retreat of the ice lobe and contact with the St.
Lawrence marine waters. Let’s take a look at the clays so well displayed
along the Button Bay State Park beach and see if we can piece together
their history.