78 GEOLUGY OF OLD HAMPSHIRE COUNTY, MASS. 



bv liydrated mica. As tlie iuterveiiing- area is almost wholly covered, the 

 line is drawn upon tiie ma]) with much doubt. 



THICKNESS. 



'V\w section gone over from the Middlefield station to the top of the 

 serie.s at the Chester line is, measured directly across the strike, 6,970 feet, 

 which, with an nverage dip of nearly 80°, would give a thickness for the 

 series of 6,897 feet, provided there be no repetitions from close folding or 

 secondary structure simulating bedding— a thing one would be very unwill- 

 ing to admit. This includes, it will be noticed, the two beds between the 

 Backet gneiss and the big hornblende lied; that is, the Hoosac and Rowe 

 schists. 



Tlir. (HESTER AMPHIH()IjIT>: AXD .SKRPEXTINES. 



The albitic mii-a-schist and the lower sericite-schist already described, 

 the hornblendic band which is separately discussed in this chapter, and the 

 upper sericite-schist and the chloritic schist next to be treated (that is, the 

 Hoosac schists to the Hawley schists, inclusive) are certainly one conform- 

 able series of beds, and form a group well demarcated from all above and 

 below. The correlation of the strata has been attended with great diflicultv, 

 owing in large part to the fact that southward along the line of .strike the 

 hvdration of the mica bect)mes less, and at last becomes inapjireciable, while 

 the chlorite also disappears and the feldspar increases in quantity, so that 

 what in Hampshire County is well-characterized hydromica and chk)ritic 

 schist becomes in Hampden feldspathic mica-schist, or even quite well- 

 marked gneiss.^ 



I have therefore found the bi'oad Viand of am]ihibolite, associated 

 abundantly with serpentine and talc, although interrupted, to form an 

 exceedingly useful horizon clear across the State. Carrying as it does the 

 unique emery vein at Chester, it is also of great interest in itself 



GENERAL DESCRIPTION. 



The amphibolite is a dark-green rock, either flat thin-fissile or ligni- 

 form, and rai-ely massive. It is almost always epidotic. Along its eastern 

 (that is, its former upper) surface at various points occur great masses of ser- 

 pentine or serpentine and steatite (the latter above the serpentine), or rarely 



' This change is caused by the great quantity of granite in and south of Blandford, from which 

 the schists are greatly soaked with feldspar. 



