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ALGONKIAN ROCKS IN VERMONT.
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far examined has all the members developed characteristically or of maximum thickness. Each member thins out and thickens along its strike in the most remarkable manner. On Nickwacket Mountain, just north of the Rutland Sheet, for example, the pebbly, micaceous quartzite member attains its greatest thickness, and the pebbly limestone as well; while in the heart of the range, east of the Chittenden flats the lower quartzite-conglomerate horizon attains its maximum development. The mica schist is best seen along the Mendon section. Provisionally, therefore, for descriptive purposes the name Mendon Series will be given these rocks.

That the relations of the different members of this series could be worked out seemed for a time a hopeless task, as it was subject to such great variations in character, and was so intimately folded, but the order given below, from less disturbed localities is correct within narrow limits. The thickness of the different beds is estimated, such estimates being based upon great familiarity with them in widely-separated localities, and under various habits due to metamorphism. The estimates are well within the limits of maximum variation.

Beginning with the Olenellus quartzite which strikes N. 5 W. to N. 5° E., the next rock, as mentioned above, descending geologically, is a mica schist. It occurs along the west base of the hill, situated in the northwest corner of Mendon. Near the quartzite it appears conformable, but as one ascends the hill, going east, the rock becomes more crumpled; two hundred feet from the quartzite the stratification has been practically destroyed, while the regional schistosity, characteristic of the Appalachian range in New England, takes its place. This induced structure, along the borders of the range strikes quite uniformily N. 10° to 15° E., dipping commonly between 60° and 80° easterly, although westerly dips are noticed. The structure of the schist consists of minute plications and larger ones many feet across, closely folded and often overturned to west. Minute faulting along the axis of the crenulations has produced the schistosity (ausweisungschiefer) which has been

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