ALGONKIAN ROCKS IN VERMONT. 409 



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 peb- 

 bly, 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 inti- 

 mately 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 



