AGE AND POSITION. 485 



and much coated by flocks of a dark-blackish chlorite ? Cleavage parallel with the base of the prism, but 

 effected with much difficulty, the crystals being too brittle to cleave with facility. In this respect the 

 mineral is similar to Clintonite and Orthite, and quite apart from mica. Color by reflected light, clove, or 

 anthophyllite-brown, by transmitted light, bluish gray. Some of the crystals are nearly transparent. 

 When closely viewed, the terminal planes generally present the iridescent-colored rings of Newton. Luster, 

 shining to splendent. Hardness, 2.5 to 3. Gravity 2.71 and 2.83 (according to Prof. Brush.) Before 

 the blowpipe its folise expand, the mineral turns silver-white, and in the highest heat passes to a per- 

 fectly white enamel or glass. Heated in a glass tube, a little moisture is evolved, attended by a feeble 

 corrosion of the glass, proving the presence of fluorine. Prof. Brush has at my request kindly deter- 

 mined approximately the following points, relative to its chemical composition : 



Silica, 47.76 



Alumina (with peroxyd of iron, 3 or 4 per cent.), 36.29 



Lime, 0.24 



Magnesia, . . . . . . 1.85 



Alkalies (by loss), 8.77 



Volatile matter, 5.09 



100.00 



From the chemical investigation, therefore, nothing has been made out incompatible with its belonging 

 to the species mica; but the impurity of the specimens analyzed, owing to the adhesion of chloritic scales, 

 renders desirable a new analysis, before we can say with confidence that its composition is identical with 

 that of mica. It is proposed as a new species wholly on the ground of physical properties. (From a letter 

 of Prof. C. U. Shepard to Prof. Edward Hitchcock, Oct. 22, 1859.) This mineral has been found at Derby, 

 Glover and Newfane 3 and may be seen in the State Cabinet under Nos. 263, 264, and 265. 



Molybdenite, or sulphuret of molybdenum. It crystallizes in short hexagonal prisms. Has a greasy feel 

 and a pure lead-gray color. Kesembles in physical characteristics, graphite, but gives a green trace on 

 porcelain. Found at Brighton, and is No. 48 in the State Collection. 



Geological Position, Equivalency and Origin. 



According to our Sections, as has been already stated, the calciferous mica schist is 

 overlaid by clay slate, and a strong presumption has been shown that the latter is of 

 Devonian age. It would follow if the strata have not been inverted that the mica schist 

 is older, though not necessarily enough older to bring it into the upper Silurian. But 

 such is the position assigned to it by the Canada Survey. (See Mr. Hunt's paper on the 

 Crystalline Limestones of North America, American Journal of Science, Vol. XVIII, p. 

 198, Second Series.) " These upper Silurian strata," says Mr. Hunt, " constitute the 

 micaceo-calcareous rocks of Vermont which Prof. Adams traced through the State to 

 Halifax on the border of Massachusetts, and they are continued in what Hitchcock has 

 called the micaceous limestones of this State (Mass.), which, according to him, pass by 

 insensible degrees into mica slate." Mr. Hunt regards the enormous mass of mica schist, 

 clay slate and gneiss, intervening between the calciferous schist of Vermont and the coal 

 formations of southeastern Massachusetts, embracing the White Mountains, as Devonian. 

 We have doubts here ; for it is at least probable that some of the clay slate along Mem- 

 phremagog is probably Devonian ; and before reaching even the coal field of Worcester, 

 in Massachusetts, we strike another band of clay slate. Moreover, the enormous thick- 

 ness of gneiss lying between the Worcester coal field and that of Norfolk County have a 

 predominant strike .quite different from that of the range between the Worcester and 



