Part 2

On Mount Mansfield some of the prominent topographic features appear to be controlled by joints. Much of the north-facing cliff on the Nose is controlled by a joint trending N. 65° W., and a similar face on the Lower Lip is controlled by a joint trending N. 60° W. Along the crest of Mount Mansfield a number of joints trend about north-south. Joints of this system in the steep cliffs on either side of the crest of Mount Mansfield have been separated further by the tendency of the rocks to creep down slope under the force of gravity. These joints form the canyons or narrow passageways which are traversed by some of the trails. On Maple Ridge at about 3300 foot elevation the trail crosses a joint trending N. 50° E. which is conspicuous for its four-foot width and the extent and the straightness of the break. A number of joints belonging to this system are found along Maple Ridge.

GLACIAL HISTORY OF THE AREA

_Introduction_

The geologic time division previous to the present one is called the Pleistocene or the “ice age.” During this time, large continental glaciers advanced over the northern part of North America several times. The cause of the ice age is not known with certainty and whether geologic history will repeat itself is a matter of conjecture. However, it is established that these vast ice sheets covered New England and that the last ice sheet melted back from the Mansfield area about 12,000 years ago.

If one stands on the crest of Mount Mansfield and looks westward over the Champlain Valley, it is difficult to visualize this entire valley completely filled with ice of the continental glacier. Yet, the evidence shows that the ice sheet was so thick that it completely covered Mount Mansfield at one time.

_Evidences of glaciation_

Two types of evidence, glacial striae and erratics, show that Mount Mansfield was over-ridden by the continental glaciation. _Striae_ are scratches in the bedrock which were produced by the sharp edges of rocks protruding from the sole of the moving glacier. These scratches show the direction in which the glacier was moving at a particular spot and the average of many readings gives an accurate value as to the overall direction of movement of the ice sheet. On the Long Trail between the Mount Mansfield Hotel and the Chin on Mount Mansfield, striations may be observed at a number of places. Some of the positions where readings were made are indicated on the map by the triangular-pointed arrows. Faint striae may be seen near the entrance of the Mount Mansfield Hotel and more conspicuous ones are visible on the west side of the roadbed of the secondary road that intersects the Toll Road just below the Hotel. Figure 7 shows a photograph taken at Drift Rock in which the striae are clearly visible.

The average trend of the striae on Mount Mansfield is about N. 50° W. The movement of the ice is presumed to have been nearly north-south down the Champlain Valley which was deepened by the erosive action of the ice. These facts seem to suggest that the movement of ice over Mount Mansfield was marginal and nearly 45° to the axis of the main ice tongue.

_Erratics_ are boulders moved and deposited by glaciers. Often these boulders are found in environments foreign to them. On the high parts of Mount Mansfield, a few boulders other than the mica-albite-quartz schist are found which have reached their present position by glacial transportation. A particularly interesting erratic is Drift Rock. One may note by referring again to Figure 7 that the glacial striae pass beneath the large boulders indicating that the boulders were not at their present position when the striae were formed. Thus, these boulders are aptly named for they must be considered erratics even though their composition is the same as the surrounding rocks. As a logical speculation it is probable that they were plucked out of the bedrock just a short distance to the northwest of their present position and it is possible that these were the very boulders that formed the striae.

Other evidence of glaciation is the presence of _cirques_ which are the high mountain basins in which mountain glaciers originate. Small mountain glaciers probably existed on Mount Mansfield, particularly in the east side of the mountain where the topography has the suggestive form of cirque-like walls and basins.

Melting of a continental glacier causes deposition of the sand and gravel scooped up and transported by the glacier. Some of this material is plastered beneath the moving glacier, some is simply let down as a blanket and terminal accumulations, and some is transported by streams of melt water to form deposits in which the sands and gravels are somewhat sorted in size by the action of the water.

The blanket type of glacial deposits probably were present over much of the Mount Mansfield area at one time, but have been removed from the upper mountain slopes by erosion. Such deposits are present at lower elevations but are only rarely discernible because of the heavy vegetation and soil cover. Sand and gravel deposits derived from post-glacial streams are located in some of the lower valleys as, for instance, along the highway north of Barnes Camp.

North of the old road and northeast of the camping area along one of the main streams on the west side of Mount Mansfield, fine-grained, sandy lake deposits occur at an elevation of about 1900 feet. The nature of the deposits indicates that they were formed in ponds marginal to the ice sheet when the continental glacier occupied the Champlain Valley but did not extend over the crest of Mount Mansfield.

DESCRIPTIONS OF INDIVIDUAL LOCALITIES

_Spruce Peak and Sterling Pond_

Spruce Peak is the mountain on the east side of Smugglers Notch. It may be reached by several trails or the ski lift. An excellent view of Smugglers Notch and the surrounding country is obtained from the summit. Near the summit along the access road to the ski lift, unweathered mica-albite-quartz schist is exposed and the folding can be clearly seen.

Sterling Pond lies to the northeast of Spruce Peak in a shallow depression along the divide of the mountain. This location is anomalous for a pond because the amount of higher land around it is so small that only a limited amount of drainage area is available for the accumulation of rain and snow. Yet, the outflow of water is almost continuous during the summer. The basin occupied by the pond was probably scoured out by the glacier.

The Sterling Pond area contains talc deposits which probably would be commercial if they were not so inaccessible for mining. These deposits have been studied by A. H. Chidester of the United States Geological Survey and a report is obtainable from the U. S. Government. The occurrence of the talc, as mapped by Chidester, is shown in the sketch of Figure 8.

Talc has the composition of Mg₃Si₄O₁₀(OH)₂ and is a soft flaky white mineral. The talc-bearing rocks in this area are white, light gray, or light green and usually are irregularly stained yellow-brown by the weathering of an iron-bearing mineral that occurs with the talc. Because of its extremely soft nature, the talc does not form prominent rock exposures. As shown by the figure, the talc can be most easily observed along the shore of Sterling Pond, south of the Green Mountain Club cabin, or along the trail to Smugglers Notch near the top of the first rise from the pond. Here the talc is exposed in the trail as low, rounded, slippery knobs of “messy looking” yellow-brown rock.

As part of the pond is underlain by talc, it is probable that the softness of the talc was a factor in the differential erosion of the basin by the continental glacier.

The talc is believed to have originated by the alteration of a body of _ultramafic_ igneous rock, which is characterized by having a low silica content and a high magnesium content. Sometime during the mountain-building period, the ultramafic igneous rock invaded the pre-existing rocks from an unknown source within the earth’s crust. It is believed that at a later date the original minerals in the igneous rock were altered to talc and other minerals by the action of hot ascending solutions composed principally of water.

MAP OF THE STERLING POND AREA FOREST BOUNDARY Green Mountain Club cabin STERLING POND To Smugglers Notch EXPLANATION Talc-bearing rock Solid areas are positions of exposures Postulated boundary of talc body beneath pond Trail To Spruce Peak From report by A. H. Chidester

The Long Trail passes by Sterling Pond, where the Green Mountain Club has erected a small cabin overlooking the pond. Figure 9 is the picturesque view of Mount Mansfield taken from the cabin.

_Smugglers Notch_

All of the rocks exposed at Smugglers Notch (Figure 10) are the mica-albite-quartz schist which locally contains garnet. The large rock boulders in the Notch were derived from the cliffs forming the walls of the Notch. The gradual processes of weathering and breaking up by freezing cause large slabs of the rock to become loose and eventually break off the cliff faces to careen down the mountainside to the valley below, just as King Rock did within historical time. At the north end of the Notch, the large accumulations of such boulders form a _talus slope_, the name for rock accumulations at the base of a cliff. The irregular stacking of these rocks have formed Smugglers Cave. Smaller openings extend further back under the “rock pile” to where the ground is considerably colder and where the heavier cold air has sunk. Drafts of this air escaping at the foot of the talus is noticeably cool.

The Smuggler’s Face, Elephants Head, the Singing Bird, and the Hunter and His Dog are freaks of nature and a product of man’s imagination. Their existence is due to the haphazard nature in which the rocks on the cliff faces have broken along joint surfaces.

The origin of the Notch is not completely known. The steep walls and the narrowness of the Notch suggest that it could not have been formed by the headward erosion of two streams or by glacial action. It seems most likely that it was formed by the erosive action of an ancient river that once flowed through the area. Because of the high elevation, the only time when such a river could have existed is when the Champlain Valley was filled with ice on the west side of Mount Mansfield, so that the normal drainage of water to the west was blocked by the ice. It is possible that the conditions were such that the water supplied by the melting glacier could only drain to the south through the Notch. After the ice retreated the drainage system was abandoned in favor of lower outlets and eventually the drainage was developed to Lake Champlain in the west. The Notch was modified by the headward erosion of the present small streams. Except for the shape of the Notch, the only evidence for this hypothesis is the occurrence of a weakly-bedded, well-sorted deposit of sand at the north end of the Notch at an elevation of 2050 feet. Such a deposit of sand is characteristic of standing water, which occurring at this elevation indicates that some vastly different drainage system must have existed in the past.

_Big Spring_

On the south side of the Smugglers Notch road at an elevation of about 1800 feet is the Big Spring which furnishes a tremendous output of cold spring water. The source of the water is not known although it is likely that, like most springs, it is derived from an underground drainage system. The spring probably originates by the seepage of water derived from the winter snows and rainfall in Spruce Mountain through a joint system within the mountain. No buried stream channels could be located between the spring and the base of the massive overhead cliffs. The belief that the spring is related to Sterling Pond is unfounded. It is unlikely that surplus water could be drained from Sterling Pond because it already maintains a delicate balance between the supply of water from rain and snow and the output to the stream flowing to the north.

_Mount Mansfield_

The summit of Mount Mansfield when viewed from a distance has the resemblance of a face with an exaggerated distance between the nose and upper lips. Accordingly, these peaks are named, from south to north, the Forehead, Nose, Upper Lip, Lower Lip, Chin, and Adam’s Apple. All these points are readily accessible by the Long Trail and the area of the Nose may be reached by the Toll Road or the Ski Lift. From all the points along the crest an excellent view may be obtained. On clear days Lake Champlain and the Adirondack Mountains in New York State may be seen to the west, and Mount Washington in New Hampshire may be seen to the east.

Of the local structures, good exposures of the mica-albite-quartz schist occur along the crest with magnetite and garnet locally abundant. The rocks on Sunset Ridge, which extends west from the Chin, can be seen clearly to be dipping at gentle angles to the west.

The Chin has an elevation of 4393 feet, which is the highest point in Vermont. Most of the schist in this area is nearly horizontal or dipping slightly to the west. However, minor folds are present everywhere and an average reading is difficult to obtain. At the summit much of the schist contains large black grains of magnetite. The summit is reached by the Long Trail along the crest of the mountain from the Toll Road, by the Long Trail from Barnes Camp via Taft Lodge, or from the west by the trail up Sunset Ridge. An excellent view of the Lake of the Clouds and the Adam’s Apple is obtained a short distance north of the summit of the Chin.

Lake of the Clouds which lies north of the Adam’s Apple and Bear Pond which lies north of Bear Head Mountain are both small shallow bodies of water. The slight depressions in which they occur were probably scooped out by the erosive action of the glacier.

Between the Chin and Mount Mansfield Hotel are a number of interesting trails. The Subway and Canyon trail on the west side of the mountain follow, for part of the way, joints in the rock which have been enlarged by the downhill slippage of the western block. Figure 11 shows the nature of one of these passageways. On the east side of the mountain, the Cliff trail passes through a similar joint called “Wall Street.” The Cave of the Winds, reached by a trail just north of the Lower Lip, has formed along another north-south joint. The block which has moved downhill has tilted into the mountain and rubble has filled the gap at the top to form the cave. Figure 12 shows the appearance of the cave as seen from the eastern slope of the Chin. This photograph shows smaller joints on the Chin which have just begun to be enlarged by slippage of the downhill block. It is possible that some of these open joints date back and partially owe their origin to glacial erosive action.

Drift Rock which is located along the Long Trail south of the Upper Lip has already been described as an erratic boulder moved by the glacier. The glacial striae may be seen in the bedrock northwest of the boulders. Garnet crystals are very abundant in these boulders and specimens of the small red garnets may be obtained here.

The Nose is easily reached along the trail from Mount Mansfield Hotel. From the summit the view is excellent to the south towards Camels Hump, which is one of the prominent peaks of the Green Mountain range. The mica-albite-quartz schist on top of the Nose has many small folds and crenulations.

South of the Forehead along the Long Trail, cliffs of an albite-rich variety of the mica-albite-quartz schist form obstacles which have been surmounted cleverly by the Green Mountain trail-markers.

In the southern part of Mount Mansfield State Forest the Long Trail passes through Nebraska Notch in the vicinity of Taylor Lodge. This notch also was formed by the erosive action of an ancient river that flowed across the mountain at this point, but which has long since been abandoned.

FOOTNOTES

[1]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 recrystallization of older rocks under conditions of high temperatures and pressures.

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_.