344 VARIETIES. 



different varieties of quartz rock, in order to ascertain how many of them contain besides 

 alumina and alkalies, silica, sufficient to produce crystals of feldspar or other minerals ; 

 and whether the mica and talcose schists associated with the quartz rock could have been 

 altered from the pure quartz, with perhaps the aid of rather more than the usual amount 

 of reagents, dissolved in the water of the period of their production. 



The quarteose aggregate is a difficult rock to name. It is homogeneous, of a dark gray 

 color, and appears to be mostly composed of silica. It slightly resembles novaculite, 

 but is an entirely different rock. The typical specimens (No. ^, in the Cabinet) are 

 from Sunderland, near the junction of the quartz rock and Stamford granite. In 

 Pittsford and Brandon, there is a great abundance of the same variety. A similar rock 

 is abundant in the red sandrock series. Careful analysis of these specimens will 

 determine their exact nature. 



The talcose schists are in a belt of rock extending from Starksboro to Ripton, with 

 perhaps repetitions. There is an excess of silica in it, and probably they contain as 

 little magnesia as the analyzed specimens from the great talcose schist formation east of 

 the Green Mountains. The mica schist (mica and much quartz) is abundant in Brandon, 

 Groshen, Mendon and Ripton. The specimens are the most characteristic in the first two 

 localities upon Section VIII. It is a singular fact that a pure quartz rock, of such 

 marked characters as the first variety, should be interstratified with so many entirely 

 different rocks. A more extended account of these interstratifications, as well as of 

 the formation in general, may be found in the detailed account of the first seven sections. 



To illustrate these varieties we introduce a section of the rocks between Bristol and 

 Lincoln (Fig. 248.) The south end of Hog Back Range, east of Bristol village, terminates 

 abruptly in a precipice four hundred feet high. It is composed of rather coarse, very 



Fio. 248. 



Section from Bristol to Lincoln. 



compact quartz rock, and its strata are beautifully shown, dipping to the east at an 

 angle of 40, gradually lessening to 28 E. In a distance of nearly two miles the 

 synclinal axis is most distinctly exhibited. It is one of the prettiest synclinals in any 

 rock in Vermont. Where the road to Lincoln crosses New Haven River (upper bridge), 

 the strata dip 18 E. and are composed of quartz layers much waved, and separated by a 

 micaceous or argillaceous film. In the extreme east part of Bristol, the quartz dips to 

 the west, rising from to 48. Here the character changes to a quartzose rock, dipping 

 east 75. There seems to be no connection between these two rocks except by a fault ; 

 but we found no evidence of this except in the sudden change of position (in a few rods) 

 with no intermediate ledges, and in the difference of lithological character. In the west 

 part of Lincoln, at the Furnace, it is the ordinary talcose schist associated with this 

 formation in other localities. At a Union store east of Lincoln village, the character 



