ALGONKIAN ROCKS IN VERMONT. 413 



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 con- 

 glomerate in the Mendon section and extending north and 

 south from there ; on the summits of Pico, Killington, Men- 

 don, Little Killington, and Blue Ridge Mountains, and in count- 

 less other localities. 



Many phases of this schist occur characterized by acces- 

 sories such as chlorite, biotite, and magnetite. An important 

 and wide-spread variety carries ottrelite in prisms and radiat- 

 ing bundles.'^ Muscovite predominates over other micaceous 

 minerals, both colorless and green varieties occurring, while 

 feldspar is only sparingly present. AH the varieties of this 

 horizon occur in great confusion, grading into one another ver- 

 tically 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 dis- 

 turbances. 



Considering 350 feet to represent the thickness of the quartz- 

 ite 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 thick- 

 ness, 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 



I This phase was described by the writer in the American Journal of Science, Vol. 

 XLIV., Oct., 1892.— An Ottrelite-Bearing Phase of a Metamorphic Conglomerate in 

 the Green Mountains. 



