Topography of the Mica Slate. 



331 



exists in that town such an alternation of strata. One of the beds of 

 this rock is partly made up of " a variety of paratomous augite-spar, 

 which cleaves into thin plates and approaches nearly in some speci- 

 mens to schiller spar. Yet " says Dr. E. " I should not call the stra- 

 tum Diallage Rock." (so it had been called) " The loose bowlders 

 which I first found were aggregates of this variety of pyroxene and 

 feldspar. I afterwards found that they came from the mica slate and 

 did not generally resemble granite." Concerning the scapolite rock, 

 placed by Dr. Emmons on the above section, he has given me no in- 

 formation. 



Topography of Mica State. 



It will be seen by the map that this rock occupies several large 

 tracts in the State. And it exists, also, in smaller quantities, associa- 

 ted in numerous places with gneiss and granite, but not shown on the 

 map. Thus the region in Northampton, Williamsburgh, Goshen, &c, 

 coloured as granite, is in fact nearly half mica slate. But it would be 

 impossible to represent the true relative position of the two rocks ; and, 

 therefore, I have coloured the whole space as composed of the predom- 

 inant rock. And the same remarks will apply to almost every other 

 range of granite that is represented in the central or western parts of 

 the State. 



The mica slate of Berkshire is chiefly of those varieties that approx- 

 imate to argillaceous and talcose slate. It there forms lofty insulated 

 mountain peaks, or continuous ranges. Saddle mountain, nearly 

 4000 feet high, and the highest point in the State, is compos- 

 ed of this rock. And so is the eastern part of Taconic range : as 

 well as nearly all those broken ranges of mountains extending Yrom 

 Lenox through Stockbridge, Great Barrington, and Sheffield. As a 

 general fact, the limestone occupies the vallies ; and this would be 

 deemed conclusive proof that this rock was deposited subsequently to 

 the mica slate, did we not find it sometimes alternating with the slate. 

 Shall we then infer, that the limestone being much more liable to dis- 

 integration than the slate, has been decomposed and abraded so as to 

 bring it down to much the lowest level? 



As we ascend the Hoosac mountain, the mica slate assumes a much 

 more crystalline aspect and appears to belong to the oldest varieties 

 of this rock. It is essentially of the same character across the whole 

 mountainous range between the vallies of Berkshire and the Connec- 

 ticut: though as we approach the latter valley, we find it sometimes 



