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 s ...

north of

Burlington, Vermont Burlington, officially the City of Burlington, is the List of municipalities in Vermont, most populous city in the U.S. state of Vermont and the county seat, seat of Chittenden County, Vermont, Chittenden County. It is located south of the Can ...

and on the eastern shore of

Lake Champlain Lake Champlain ( ; , ) is a natural freshwater lake in North America. It mostly lies between the U.S. states of New York (state), New York and Vermont, but also extends north into the Canadian province of Quebec. The cities of Burlington, Ve ...

. It is publicly accessible via a trail network and sits on land owned by the Episcopal Diocese of Vermont. The site is of geologic significance for its spectacular exposure of a thrust contact between the

Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...

-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 extending from southern Quebec, down through western Vermont in the Champlain Valley, and into eastern New York in the Catskills/Hudson Valley. This east dipping thrust fault transports Cambrian-Ordo ...

which formed during the

Taconic Orogeny The Taconic orogeny was a mountain building period that ended 440 million years ago (Ma) 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 ...

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

structural geology Structural geology is the study of the three-dimensional distribution of rock units with respect to their deformational histories. The primary goal of structural geology is to use measurements of present-day rock geometries to uncover informati ...

feature in all of

New England New England is a region consisting of 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 (state), New York to the west and by the ...

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. I ...

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

Dunham Dolomite

The Dunham Dolomite is a Cambrian dolomite 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

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 by ...

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}