DESCRIPTIONS. 469 



Prelmite. This mineral belongs to the Trimetric system of Dana, usually being found in right rhombic 

 prisms. These crystals are usually small ones that are implanted on globular or reniform masses, or 

 incrustations. It is a hydrated silicate of alumina, lime and iron. In color it is of some shade of green. 

 In Vermont it occurs at Bellows Falls and Vernon. Its numbers in the Cabinet are from 318 and 321 

 inclusive. 



Chiastolite. A variety of Andalusite, to be described below. 



Fibrolite, or Sillimanite, is a mineral generally found in long prisms or fibers, though sometimes massive. 

 The primary form is an oblique rhombic prism from 98 to 110. It is a silicate of alumina resembling 

 kyanite. Color hair-brown or grayish. It has been found at Saxton's River. 



Scolecite. Monoclinic, in radiating balls, which are often quite compact at the center. The color is gener- 

 ally white, but sometimes yellowish, blue and red. It is often called a lime mesotype. Its composition is 

 silica, alumina, lime and water. It has been found at Westminster. 



Stilbite. A zeolitic mineral in cavities and seams, with radiating structure. Prevalent color white, 

 .with shining luster. Primary form right rectangular prism. Composition hydrated silicate of lime and 

 soda. It has been found at Rockingham. 



Finite. See lolite below. 



Andalusite. A flesh-red or pearl-gray mineral, and known as Made or Chiastolite and Hollow Spar. Its 

 primary form is that of a right rhombic prism, and its chemical composition a silicate of alumina, with a trace 

 of iron. The variety Chiastolite seems to be owing to impure crystals of differing hardness, which are 

 arranged symmetrically about the axis and edges, giving a beautiful variety of figures to the crystals when 

 cut vertically and polished. It has been found at Saxton's River and Bellows Falls. 



lolite or Finite (above), and above twenty other varieties, according to Professor Shepard. It is, in pri- 

 mary form, a rhomboid, and its secondary form is often a hexagonal prism. Its composition is silica, alumina 

 manganese (oxyd), oxyd of magnesia, and oxyd of iron. The color varies from blue, brownish-yellow to 

 yellowish-gray. 



Finite seems to be an altered form of lolite. This is a dull, greenish-gray, and is nearly opaque. It is 

 also very soft. While the hardness of lolite is from 7 to 7.5, Finite is frequently no higher than 3. This 

 also contains soda and potash in addition to the other ingredients. It has been found at Chittenden and 

 Rockingham. 



Geological Position, Origin, and Metamorphism.* 



If we were to limit the term gneiss to a foliated rock highly charged with feldspar, 

 Vermont would afford but little of it. The deposit marked as gneiss upon our map, which 

 intercepts the calciferous mica schist, and seems to take its place, from Hartland to the 

 south line of the State, would constitute its largest deposit. But on traversing the Green 

 Mountains, almost through the entire State, we find them in a great measure made up of 

 a schistose rock, much of which we should refer to mica schist or talcose schist. Yet it 

 contains more or less of feldspar, and sometimes passes into distinct gneiss. Professor 

 Adams called it Green Mountain gneiss ; and for a time we were inclined to refer it to 

 that variety of mica schist which McCulloch describes as containing some feldspar. But 

 following the rock on the line of strike, and sometimes crosswise, we often find very dis- 

 tinct gneiss ; and hence we concluded to call the whole gneiss, where any considerable 

 quantity of feldspar occurs interfoliated. But such a character is quite indefinite, and no 

 two observers would probably fix the limits of such gneiss in the same place. Hence we 

 consider the color denoting gneiss along the Green Mountains as the most unsatisfactory 

 of all those upon the map. Moreover, those layers of the rocks, on both sides of the 



*By E. Hitchcock, Senior, 



