lar grains. Both muscovite and biotite are present. Epidote shows its high index of refraction and strong double refraction. It cannot be assumed to be an alteration product, because no partially decomposed calcium-iron mineral is present. Chlorite is present in only a few instances. There is a series of batholiths of this description, ranging from the "gneiss" of Hinsdale and Vernon to the so-called Bethlehem Group beyond Littleton. Some of them carry beds of limestone, so as to suggest the gneissic area from Marlboro to Reading, supposed to be a duplication of a part of the Green Mountains.

DYKES.

Some dikes have been examined within this area, but there is no time in which to describe them. Such are the diabases of Crafts Hill and Quechee Gulf, the camptonite of West Norwich, the diorites associated with the green schists, immense veins of white quartz, apophyses from the Lebanon granite and the granites of West Lebanon.

SURFACIAL GEOLOGY.

Plate XXIXa.

The area of the Hanover quadrangle abounds in illustrations of glacial action and erosion. After the elevation of the land immense blankets of rock have been worn down, peneplains formed, and enough material to make a small continent been carried to the sea and buried therein. The longer this stupendous work has been studied the greater is our conception of the magnitude of the operation. The earlier geologists could not understand how glaciers could have been so effective, judging from the diminutive effects produced by such glaciers as those of the Alps of Switzerland. They could not conceive of an ice sheet of continental dimensions, though not shrinking from a belief in a submergence fully as large. In our field, we can describe the till, moraines, striæ, diverse movements of the ice sheet, local glaciers, eskers and terraces and still not be ready to explain why such a glacial winter should have been intercalated into our history. Vermont had been enjoying a genial climate, sustaining a growth of hickories, giant beeches, the New England cinnamon, and unique conifers, and of course the singular mammals that roamed about these forests, but the great climatic change obliterated every sign of their exuberance except a few tons of

Brandon lignite. Though obliged to change the character of our studies, we find a compensation in the many interesting features of our history, brought to light by investigating the markings on the rocks and the deposits of earth transported in various ways.

Perhaps we may as well commence our story with some description of this wide sheet of till or ground moraine formerly spoken of as drift. The familiar expression hardpan will convey to people generally what this deposit is—a compact assemblage of materials without structure, but when dissected carefully found to be made of stones that must have been transported in particular directions, and divisible into two parts. The lower portion contains stones that have been transported great distances, are scratched according to method (glaciated), are of a bluish cast and very compact. The upper portion carries rough stones not glaciated, such as have come only short distances, the material is loose and of a reddish brown color. Plate XXVIII represents an excavation in this till upon Bragg's Brook, in Norwich, nearly a hundred feet high, kept fresh by the stream of water at its base. The absence of stratification is very apparent. The stones that are in the lower portion are recognized as having been derived, some of them, from a distance of forty miles. None of them are very large and the substance in which they are imbedded is a clay, very plastic when wet and evidently made by the pulverization of the slates and schists of the neighborhood and retaining its original color. Many prefer the name boulder clay to till for this portion. The upper reddish part may be only a strip of light color beneath the turf, and it has all the characteristics mentioned above. As the stream has been wearing down this bluff ever since the date of its accumulation, it is not difficult to believe that the valley was once filled with it from edge to edge on the top.

Our view of the origin of the till is that it is the ground moraine of the continental glacier, that it was crowded along beneath the ice generally, and for that reason the stones are of small size. The compactness is due to the pressure exerted by the weight of the ice, probably a mile in thickness. When the ice had been melted the pressure was removed and the upper portion consisted only of the debris that was in and upon the ice, which is confessedly the latest material brought, and falling through the water rests upon the compact mass and the fragments lie in stable equilibrium, unlike the stones beneath, which have been forced into unnatural positions.

The water rusts the stones and consequently this upper till is of

a reddish brown color. In other words, the iron in the lower part is ferrous, in the upper part ferric. No doubt oxidation may be produced by the natural seepage of the water into the hardpan. That process cannot explain the roughness of the erratics and their derivation from localities near at hand. If one should now climb to the top of this hill, he would find a broad, smooth surface fitted for tillage, extending indefinitely to the northwest. The original dissected surface has been evened up by the ice acting as a gigantic scraper, and this feature is common over the whole quadrangle.

Let us look more carefully at this sheet of till as it rests on the south side of the valley of White River, through the central part of Hartford. Low down the edge is bluff-like because of erosion, higher up there is the same smooth surface extending to the crest of the ridge—all of this same till—and quite free from erratics. Plate XXIX represents a bluff of it exposed like that in Plate XXVIII by erosion at its base. It is at Centerville on the south side of the river, and at the mouth of a small stream draining the hillside from the Woodstock railroad and the western carriage road to Quechee village. Here may be found stones consisting of the red sandrock of Burlington, that have traveled about sixty miles. These were not seen on Bragg's Brook, because the direct line of the glacial current did not extend so far north. White River Valley is the most northern point which these red stones fell upon, and they may be found in greater or less abundance all the way from Centerville to Massachusetts. The best locality I have seen for them is at the deep railroad cut between Hartford and Quechee, which corresponds in structure to what has been exhibited in Plates XXVIII and XXIX.

The level nature of the surface of the till is well shown just opposite Centerville, where two houses are located at the altitude of 627 feet, 267 above the river. This flat is the top of the till exposed in Plate XXIX, so that the thickness of the sheet itself may be stated at something rising 200 feet. Its width along the Quechee road is a quarter of a mile where it has been cut through. This is an average section of the dimensions of this till sheet along the south side of White River. Looking at it from a proper vantage point this smooth, even surface may be seen to extend up to the crest of the ridge and two conclusions may be drawn respecting it; first, the leveling down was effected by ice, and, secondly, the movement was subsequent to that which left the ground moraine. This point may be better appreciated by the discovery that glaciated stones in the surface of the