CHAPTER AM. 



THE LOWER SILURIAN SERICITE-SCHISTS AND AMPHIBO- 

 LITES ON THE WEST SIDE OF THE VALLEY. 



THE HOOSAC SCHIST = THE AL,BITIC MICA-SCHIST.' 



Next east of and next above the Becket gneiss a continuous band of 

 feldspathic mica-schist, often sericitic, crosses the State, and the irregular 

 western boundaries of the counties here studied inchide three portions 

 thereof within Monroe, Middlefield, and Blandford. while a loop of the 

 same rock is brought up in the Granville anticline. 



The bed has so decidedly the habit of a mica-schist and is so closely 

 associated with the mica-schist next above that I have chosen the name 

 ''albitic mica-schist" rather than gneiss for it. At its northern extremity, 

 however, the amount of feldspar increases and the rock becomes a gneiss, 

 porphyritic with small crystals of albite. It is shown below that this is 

 the Green Mountain gneiss of Adams. At the base of this formation a 

 dark, highly garnetifei'ous mica-schist forms the passage bed from the 

 Becket gneiss to the main portion of the series. The latter has the habit 

 of a mica-schist, although it is generally quite feldspathic. The small, 

 rounded crystals of albite scattered porphyritically in the mass have often 

 in crystallizing cemented several grains of quartz together. Both micas 

 are present, and the rock is generally quite dark from the abundant biotite. 

 It shares with the following formation the greasy feel from the hydration 

 of its muscovite. Where it crosses the Boston and Albany Railroad the 

 basal garnetiferous schist has disappeared, and the whole series is from 

 the base up a light-gi-ay, quartzose sericite-schist, porphyritic with many 

 small, rounded albite crystals, which often cement the quartz grains. 



' Base of the talcose schist of President Hitchcock. 



