MAGNESIAN SLATE. 153 



I believe it to be a variety of talcose slate ; and wiien the wliole rock is taken into view, I con- 

 ceive it to consist mostly of talc ; in addition to which, we have quartz, generally the milky 

 variety, and chlorite, both in masses. Some diversity of composition is still to be found where the 

 slate is in proximity to limestone, or the granular quartz. There is no great variety in this rock, 

 however, whether we examine it on the borders of the sparry limestone along the New-York line, 

 or alon<'' the edge of the Hoosic mountain range, almost in contact with gneiss. In this entire 

 belt it is grey, light or dark, with a silvery or slightly pearly lustre ; the feel is never harsh 

 or gritty, unless when near or enclosed in the granular quartz. Sometimes it is plumbaginous, 

 or contains graphite in a fine state of subdivision, in sufficient quantity to soil the fingers ; 

 but it never occurs in crystalline scales, or in a state in which there is the least metallic lustre. 

 It may be seen to differ in many respects from the talcose slate of the gneiss system ; being 

 softer, and containing less silex, but it differs, as has been stated in the preceding pages, from 

 the slates of the Primary system, by the absence of serpentine and hornblende. 

 • There are a few minerals contained in this rock, which give it a primary character, viz. 

 octahedral iron and needle-form schorl in crystals, which are disseminated in the rock in a 

 mode similar to those in mica or talcose slate. These instances are, however, rare, and may 

 not materially affect our opinions. 



The section No. 49, exhibits the relalions of this rock to the other members of the Taconic 

 system : 



49. 



1. Slate of Saddle mountain. 3. Granular quartz. 5. Sparry limestone of Petersburgh, N. Y. 



2. Limestone of its base. i. Magnesian slate. 



This rock, it will be seen, occurs in mountain masses, and is without doubt the most 

 important member of tliis system. The same remarks are appropriate to this rock when its 

 number of distinct belts are considered, as were made in relation to the limestone ; that is, it 

 is not easily determined whether there is more than one mass, or two, or three ; the appear- 

 ance of it in separate and apparently distinct beds or belts, being the effect of as many diffe- 

 rent uplifts. There is probably two or more distinct masses, which, could we avail ourselves 

 of the light which organic remains furnish, would enable us to determine the question with 

 great truth and exactness. 



This rock forms the great mass of the Taconic mountain. The sparry limestone plunges 

 into it at its base ; and above, on the west side, the range rises in steep declivities. Along 

 the summit, milky quartz abounds in irregular masses of every form ; they contain chlorite, and 

 the oxide and carbonate of iron. Scarcely any change in mineral characters is ever found to 

 have taken place. Traced from the Highlands of New- York, along the borders of the State, 



Geol. 2d Dist. 20 



