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.
Figure 7. Drift Rock, glacial erratics along the Long Trail on Mount Mansfield. Note the glacial striae trending away from the viewer and passing beneath the boulders.
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.