VAKIETIES. 437 



Passing to the lower series, the magnesian slate, the uppermost member, is a species of 

 talcose schist, having an unctous feel, owing to the presence of magnesia. It remains to 

 be proved that the substitution of alumina for magnesia in those specimens which have 

 been analyzed, extends to the whole mass. This slate is generally of a light gray color, 

 with greenish patches. Often it is darker colored, from the decomposition of sulphurets. 

 In the north part of the State, talcose conglomerates and quartz rock form a very large 

 constituent of this member. A few beds of limestone occur in it. 



The Stockbridge limestone is silicious and dolomitic in its eastern or lower portions, 

 and is largely composed of pure limestone and marble in its upper portions. There seems 

 to be a gradual change from pure quartz below to limestone above precisely as the 

 Potsdam sandstone changes into the Chazy limestone, through the interval of the calcif- 

 erous sandstone. There may be a few narrow beds of slate in some portion of this series. 

 The limestone is generally white, but there is every grade of color between white, black 

 and gray. Occasionally it has a bluish color. 



The granular quartz is generally pure, often hyaline, homogeneous, and finely granular 

 quartz rock. It is rare to find any other mineral mixed with the quartz. A very few 

 scattering shales of mica or talc may sometimes be seen. The most prominent varieties 

 of this formation are these : 1. A conglomerate. 2. Brown granular quartz rock. 3. 

 Fine white friable sandstone. 4. Talcose schists and grits of several kinds. Large beds 

 of limestone are connected with the other varieties, which seem to form a part of the 

 series as much as the schists. Whether Prof. Emmons would consider them as the Stock- 

 bridge limestone intricately plicated with the quartz rock, or a part of the granular 

 quartz series, we cannot conjecture. 



Distribution of the Taconic rocks in Vermont. The western line of the Taconic system 

 begins west of Highgate Springs, at about the east side of Hog Island, (of course then 

 the Trenton limestone at Highgate Springs is merely an outlier resting upon the Taconic 

 slates.) The western line is in the bottom of Lake Champlain from McQuam Bay in 

 Swanton, passes through the west end of Colchester Point, including probably the rocks 

 on Appletree Point in Burlington. It next touches the shore in the west part of Shel- 

 burne. From Shelburne to Orwell, it follows the course of the range of red sandrock, 

 being always a short distance west of the top of a range of mountains, which are capped 

 by Potsdam sandstone and calciferous sandstone (Red sandrock series.) The line turns 

 from Orwell village to the northwest part of Benson, quite near to Lake Champlain. 

 It turns a trifle easterly, passes through West Haven Center, leaving Vermont near the 

 mouth of Cogman Creek. Two and a half miles east of Whitehall, N. Y., east of the 

 mountain, these slates appear exposed in a ravine. This westerly line is the route of a 

 great fault, which extends from Canada to Alabama. 



The east border of the Taconic rocks coincides probably with the eastern limits of the 

 talcose conglomerates and quartz rock, as delineated upon the map, running through the 

 towns of Franklin, Sheldon, Fairfield, Fairfax, Westford, Essex, Jericho, Richmond, 

 Huntington, Starksboro, Lincoln, Ripton, Goshen, Chittenden, Mendon, Shrewsbury, 

 Wallingford, Mount Tabor, Peru, Winhall, Manchester, Sunderland, Glastenbury, Wood- 

 ford, and Pownal. In the south part of the State, this line runs along the base of the 

 principal range of the Green Mountains, but at a considerable distance west of this range 



