Page:The Journal of geology (IA journalofgeology21894univers).pdf/429

ness is not less than 700 feet. Where an excess of shearing motion has operated, a well-laminated schist has resulted, examples of which may be seen at the base of the conglomerate in the Mendon section and extending north and south from there; on the summits of Pico, Killington, Mendon, Little Killington, and Blue Ridge Mountains, and in countless other localities.

Many phases of this schist occur characterized by accessories such as chlorite, biotite, and magnetite. An important and wide-spread variety carries ottrelite in prisms and radiating bundles.^[1] Muscovite predominates over other micaceous minerals, both colorless and green varieties occurring, while feldspar is only sparingly present. All the varieties of this horizon occur in great confusion, grading into one another vertically and along the strike. In my notes the most schistose variety has been called Killington schist, and this with the green gneissose phase are the two most common occurrences of the rock. It seems preferable to adopt the name conglomerate-gneiss for this horizon as it is descriptive of its present mineral constitution and suggestive of its past history. All the evidences of profound dynamic movement observed in this series are observable in the quartzite along the Mendon section. In fact, no rock in the Mendon series bears evidence of so great disturbances.

Considering 350 feet to represent the thickness of the quartzite and conglomerate at this point, the total thickness of the section is approximately 1,300 feet. It is probable that in some localities there may be 2,000 feet of strata, and in the northern part of the State no doubt the formation is much more greatly developed. As a whole it is subject to great variations in thickness, and may decrease to two or three hundred feet, as on the south end of Bear Mountains in Wallingford. The relations of the conglomerate-gneiss horizon to the underlying rocks will be