136 



from the finest to the coarsest, medium varieties predominating ; 

 and, though usually distinctly stratified, the bedding is fre- 

 quently so obscure, and the texture so coarse or crystalline, 

 that the rock becomes the indigenous granite. The gneiss is 

 nearly always more or less micaceous, and, when of a fine tex- 

 ture, often passes through an excess of mica, into mica slate ; 

 and it is rarely hornblendic, very rarely largely so. 



There can be little doubt, as was long ago pointed out by 

 Prof. Hitchcock,^ that the gneiss of Plymouth County ex- 

 tends easterly under the superficial deposits of Barnstable 

 Coimty, forming the axis of Cape Cod as far east at least as 

 Orleans. 



At all points east of the Worcester and Dracut range of 

 granite, and north of the long peninsula of Huronian rocks ex- 

 tending from Concord to Westborough, the gneiss dips towards 

 the north-west and west. The dip is usually steep, averaging 

 perhaps 70°, but ranging from 20° to vertical. South of the 

 Hiu'onian peninsula just mentioned the gneiss dips at moderate 

 angles, average about 30°, to the north-east; and this dip 

 continues through Rhode Island. The gneiss in Bristol and 

 Plymouth Counties has for the most part gentle dips to the 

 north and north-west ; and on the western border of the 

 Nashua Valley the dips are easterly, ranging from 10° to 30°. 



Mica Slate. — East of the Connecticut Valley there is in 

 Massachusetts, disregarding a few small patches which are 

 mainly local variations of the gneiss, only one area of mica slate ; 

 this enters the State on the north-east, in Amesbury and Haver- 

 hill, with a breadth of seven or eight miles ; and extending 

 thence south-westerly along the Merrimac it becomes narrower, 

 and in Methuen, where it meets the north-eastern end of the 

 Worcester and Dracut range of granite, it appears to divide into 

 two bands, which continue, one on either side of the granite, in 

 the same general direction. The southern band leaves the Mer- 

 rimac at Lowell, and, with a breadth varying from one to two 



1 Final Report on the Geol. of Mass., p. 682. 



