Vermont

Mt. Mansfield (Chin)
       7 ½’ X 15’ quad: Mt. Mansfield, VT
       Chittenden County
       Long Trail
       Green Mountains

Metamorphic (metamorphosed sedimentary)
4,393 ft (1,339 m)


Mt. Mansfield's Nose and Chin as seen from the east across Spruce Peak.


Mt. Mansfield as seen from the west on Lake Champlain.

Bedrock: Fayston Formation

Late Proterozoic to Cambrian

Silver-green, medium grained, quartz-chlorite-muscovite-garnet schist with abundant quartz veins. The rocks were originally deposited as sediments during rifting of the Laurentian continent, and thrust westward during the Taconian Orogeny, the Middle Ordovician collision between Laurentia and an island arc complex. Mt. Mansfield lies near the crest of the Green Mountain anticlinorium such that the foliation at the summit dips quite gently. The rocks were metamorphosed to garnet grade in the Taconian, and arched into the anticlinorium under lower-grade conditions during the Acadian orogeny.

Surficial Geology: The summit area is largely bare bedrock, smoothed and striated by glacial erosion, evidence that it was overtopped by Pleistocene glaciers. Smugglers Notch, a deep cleft across the Green Mountains northeast of the Chin, was likely formed by erosion along joints. The mountain itself is said to resemble a human profile tilted slightly back such that the Chin is the highest point at the north end, with the Nose and Forehead to the south (in Lamoille County). A fascinating feature called Cantilever Rock is worth a side trip off the Sunset Ridge Trail: a 40-foot long obelisk-shaped rock projects horizontally into space 60 feet above the ground. The slab of rock is bounded above and below by smooth joint surfaces, and it is easy to visualize how the rock rotated out away from the cliff. Another side trail called the Subway, closer to the summit, affords a fun scramble through jumbled rocks along a line of vertical joints.

Soil Series: Bedrock and Lyman rocky loam: Shallow, somewhat excessively well drained, friable, dark reddish-brown channery loam with a thin, very dark gray A horizon, formed in glacial till derived from mica schist under alpine vegetation and scrubby spruce-fir forest. In the last thirty years the Green Mountain Club has promoted preservation of the soils and plants on Mt. Mansfield’s summit by discouraging off-trail foot traffic. Recent work by a student at Middlebury College has shown that the meager soils between outcrops of bedrock have been produced in part by weathering of bedrock, rather than being solely accumulations of organic material. She came to this conclusion because the inorganic portion of the alpine soils shares similar bulk mineralogy and chemistry with the underlying bedrock. Furthermore, the less soluble elements are more abundant in the deeper soil horizons.

Additional Photos:


Flat foliation in schist at the Chin summit

Selected References:

  • Christman, Robert, 1959, Bedrock Geology of the Mt. Mansfield [15’] Quadrangle, Vermont: Vermont Geological Survey Bulletin No.12., 1:62,500.
  • Farrugia, Gianina, 2005, Investigating alpine pedogenesis on Mt. Mansfield, Vermont: The Green Mountain Geologist, v.32, no.2, p.10, Vermont Geological Society.
  • Thompson, Peter J. and Thelma B.Thompson, 1999, Digital Bedrock Map of the Mt. Mansfield 7½’ Quadrangle: Vermont Geological Survey Open-File Report VG99-3, 1:24,000. See the following maps-on-line link: http://www.anr.state.vt.us/dec/geo/images/digitalofrs/mtmansfieldweb.jpg

Other suggested sources of information:


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