Topography of Talcose Slate. 



355 



take not, it is in this decomposed carbonate of iron, that native gold 

 occurs. (Nos. 833, 834.) 



8. Talc, Quartz, and Hornblende. The latter mineral is in dis- 

 tinct though imperfect crystals, scattered through the rock ; but it 

 occurs in such quantity, and over so great an extent of country, that 

 it seems proper to make this a distinct variety. It is found along the 

 eastern margin of the talcose slate formation, near its junction with 

 the mica slate in Hawley and Plainfield; and it sometimes passes into 

 distinct hornblende slate. (Nos. 835 to 839.) 



9. Talc, Feldspar, and Quartz. This variety is intermediate 

 between talcose slate and gneiss ; and differs from the latter rock only 

 by the substitution of talc for mica. It is obviously, however, a rock 

 more mechanical in its character than gneiss ; the feldspar existing 

 in coarse grains. This description applies particularly to this rock 

 in Smithfield, R. I. (No. 840.) But in Hawley the feldspar is scat- 

 tered in crystalline masses through the rock, forming a distinct por- 

 phyritic, talcose slate; (No. 841,) and it is almost destitute of strati- 

 fication. 



Topography of the Talcose Slate. 



The principal deposit of this rock in Massachusetts, is in the 

 midst of the mica slate of the Hoosac mountain range. It occupies 

 a very elevated portion of that range, and is there obviously one of 

 the oldest of the stratified rocks. I have traced this rock 20 or 30 

 miles into Vermont, where it is associated with limestone and gneiss 

 on the eastern slope of the Green Mountains ; and probably it ex- 

 tends much farther north. In Massachusetts it is most perfectly de- 

 veloped in its characters in Hawley and Plainfield ; where it is sev- 

 eral miles wide. Proceeding southerly this formation becomes nar- 

 rower, and at length appears to terminate near the southern part of 

 Becket ; at least I have not observed it farther south, and between 

 Chester and Becket it is only a few rods wide, alternating with mica 

 slate and hornblende slate. The chlorite slate forms a narrow stra- 

 tum along the western margin of the talcose slate, and I have not ob- 

 served it quite as far south as the talcose slate. But northerly I have 

 traced it as far as Whitingham, Vt., although I have not seen it in 

 every place where I have crosed the Hoosac range. But being a re- 

 markably distinct stratum, I have little doubt that it does extend as 

 far, at least, as it is represented on the map, and that it is continuous ; 



