352 C. L. Whittle — Main Axis of the Green Mountains. 



the V- shaped area of pre-Carabrian rocks mapped by Hitch- 

 cock, occurring along the trend of the range indicates a fall- 

 ing away of the axis to the north. 



Section VI of Hitchcock passes through Mendon and Sher- 

 burne where the border rocks are exposed capping the sum- 

 mits of the highest peaks, furnishing a key to the structure 

 along this line where most of the detailed work has been done. 

 As a working hypothesis the following sequence of meta- 

 morphosed elastics, exposed in continuous section on the west 

 slope of Blue Ridge Mountain making the border series, has 

 afforded positive results in deciphering Green Mountain struc- 

 ture : descending geologically from the base of the Olenellus 

 quartzite the next rock is a bed of chloritic mica schist* very 

 much crumpled, hence its thickness is difficult to obtain. It 

 seems always to be present in this part of the State, although 

 on Clarksburg Mountain in Massachusetts, lower Cambrian 

 quartzite lies directly upon granitoid gneiss without any clastic 

 series intervening. The question of the relationship between 

 the mica schist and the Olenellus horizon will not be discussed 

 at this time. In Vermont the mica schist at a minimum has a 

 thickness of not more than fifty feet and in places it is cer- 

 tainly five hundred feet in thickness and may reach a thou- 

 sand feet. Below the schist comes in several hundred feet 

 of micaceous quartzite locally assuming a schistose phase, 

 or on the other hand becoming massive and compact. All 

 phases carry numerous pebbles of orthoclase, microcline and 

 quartz, feldspar being most abundant. The quartzite horizon 

 also varies greatly in thickness and may thin out entirely. 

 Due east of Rutland a micaceous phase probably attains a 

 thickness of four hundred feet. Next below is a white crys- 

 talline limestone, carrying the same varieties of pebbles, some 

 phlogopite secondarily developed, and graphite. It locally 

 thins out first passing through micaceous phases. In places 

 areas have escaped recrystallization and are still blue in color, 

 promising with careful search to yield fossils. Two hundred 

 feet may be postulated as its maximum observed thickness in 

 the heart of the range. Another thin bed of micaceous 

 quartzite occurs below this containing one or more beds of 

 interstratified limestones ten or fifteen feet in thickness. These 

 lie upon the lowest member of the border series, the meta- 

 morphic conglomerate horizon which is separated from the 



* Dana has used the name hydro-mica schist for similar rocks occurring in 

 Massachusetts. Although it seems for many reasons the best name that has yet 

 been proposed it does not seem generally to have been adopted. Microscopically 

 the schist is composed mainly of chlorite and muscovite with varying proportions 

 of sericite and biotite; quartz is nearly always present, but in extremely fissile 

 phases it is practically absent. On the other hand varieties occur in which the 

 micaceous constituent is much less in quantity. 



