Lone Rock Point is a

promontory A promontory is a raised mass of land that projects into a lowland or a body of water (in which case it is a peninsula). Most promontories either are formed from a hard ridge of rock that has resisted the erosive forces that have removed the so ...

north of

Burlington, Vermont Burlington is the most populous city in the U.S. state of Vermont and the seat of Chittenden County. It is located south of the Canada–United States border and south of Montreal. As of the 2020 U.S. census, the population was 44,743. It ...

and on the eastern shore of

Lake Champlain , native_name_lang = , image = Champlainmap.svg , caption = Lake Champlain-River Richelieu watershed , image_bathymetry = , caption_bathymetry = , location = New York/Vermont in the United States; and Quebec in Canada , coords = , type = , ...

. It is publicly accessible via a trail network and sits on land owned by the

Episcopal Diocese of Vermont The Episcopal Diocese of Vermont is the diocese of the Episcopal Church in the United States of America in the state of Vermont. It was the first diocese in the Episcopal Church to elect a woman, Mary Adelia Rosamond McLeod, as diocesan bishop. ...

. The site is of geologic significance for its spectacular exposure of a thrust contact between the

Cambrian The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...

-aged Dunham Dolomite and the Middle-Ordovician Iberville Shale. The thrust fault exposed at this location is regionally called the

Champlain Thrust The Champlain Thrust is a 200-mile long fault (geology), fault extending from southern Quebec, down through western Vermont in the Champlain Valley, and into eastern New York (state), New York in the Catskill Mountains, Catskills/Hudson Valley. Th ...

which formed during the

Taconic Orogeny The Taconic orogeny was a mountain building period that ended 440 million years ago and affected most of modern-day New England. A great mountain chain formed from eastern Canada down through what is now the Piedmont of the East coast of the Unit ...

. At this site, the stratigraphic throw of the Champlain Thrust measures about 8,850 feet. The site is arguably the most visited structural geology feature in all of

New England New England is a region comprising six states in the Northeastern United States: Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont. It is bordered by the state of New York to the west and by the Canadian provinces ...

and is featured in many structural geology text books as a classic example of a

thrust fault A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. If ...

.Billings, M. p., 1972, Structural Geology (3rd Ed.); Prentice-Hall, 606 p.

Dunham Dolomite at Lone Rock Point

The Dunham Dolomite is a Cambrian

dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...

that is exposed in the hanging wall of the Champlain Thrust Fault at Lone Rock Point. This unit was initially deposited in a warm, shallow sea environment as a platform carbonate. Well-exposed mullions at the base of the dolomite plunge about 15 degrees southeast, indicating transport direction (headed toward the modern lake). The light colored rocks along the shoreline are blocks of dolomite that have fallen after the shale eroded away.

Iberville Shale at Lone Rock Point

The Ordovician Iberville Shale was likely deposited in a deeper marine environment and consists of fine-grained

clastic Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus,Essentials of Geology, 3rd Ed, Stephen Marshak, p. G-3 chunks, and smaller grains of rock broken off other rocks ...

materials.^{/sup> Slip surfaces within the Iberville Shale seen at Lone Rock Point often contains calcite

Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...
slickenlines along the planar thrust surface. Overlying pressure has led to a high degree of vertical faulting and calcite dissolution (white banding) throughout the unit. The top-most layer of the shale has been eroded away.

References

{{Coord, 44.490309, -73.248739, display=title

Geography of Burlington, Vermont
Landforms of Chittenden County, Vermont
Tourist attractions in Burlington, Vermont
Geology of Vermont}