Page:The Journal of geology (IA journalofgeology21894univers).pdf/441
tions, now in the geological exhibit of the Agassiz Museum, Cambridge, Massachusetts, Fig. 2. A fair percentage of the pebbles are of a composite nature (gneiss) and as would be expected, they have yielded most easily to the deforming forces. They now form in large part with secondarily-developed green muscovite, feldspars and cement of the pebbles, the more schistose folia of the rock. Stretching and flattening have resulted from a force operating along the plane of bedding in the direction of dip. The pebbles have been elongated most in an east and west direction, and their perceptible flattening indicates that this elongation took place under enormous load; an environment unlike that of the pebbles at South Chittenden, which have undergone elongation without marked lateral yielding. The environment factors here were probably extreme load, a force tending to push the rock as a whole towards the west, and the presence of water charged with inorganic compounds that promoted the alteration of the clastic feldspar material, already weakened by sub-aërial decay to more stable compounds under the changed environment, and at the same time cementing the mosaic of quartz and feldspar grains resulting from the enforced granulation into a coherent rock. It seems unnecessary to postulate a high degree of temperature to account for these phenomena; nor has plasticity, as properly defined, played any part in the deformation of the quartz and gneissic pebbles.
At North Sherburne a conglomerate occurs of considerable thickness and extends south to Ludlow, a distance of twenty-five miles. It is fully as persistent on the east side of the range in the area under discussion, as on the western, and, although some phases are unlike the western belt as a whole, it may be safely correlated with the conglomerate-gneiss horizon making, as first suggested by Adams, an anticlinal axis between Plymouth and Rutland valleys.
The question of the relations of the conglomerate-gneiss to the lower or Mount Holly rocks, has been most carefully studied on the western side of the range where the country is more open. At East Clarendon; just north of South Chittenden, and at Hitch-