THE COLES BROOK ANTICLINE. 



23 



The Coles Brook anticline extends north into Middlefield mure th:ni a 

 mile and a half, following the brook bed for a hundred rods. It is well 

 exposed just south of Factory villag-e, l)y the roadside, for a Ion- distance 

 south of the schoolhouse. Large bosses of the coarse limestone appear 

 here, flanked on the west by the Lee hornblendic gneiss. 



A still more instructive section is exposed lialfway between the two 

 localities mentioned above, where the road going west from Factory Brook 

 up onto the high ground crosses the limestone near the site of H. Hawes's 

 house (now destroyed). In the V)are hill opposite this site the limestone 

 and the o-reen actinolitic rock derived from its alteration are abundantly 



HinsilaleGnMs N30'E.7SW 

 zsrr 



Fia. 2.— Detailed sectiou "f the limt'stone at Coles Brook. 



exposed in vertical strata, and the white Becket gneiss can be seen mantling 

 over it in clear imconformity, starting with steep west dip on the west side 

 of the hill, becoming horizontal on the top, and dipping easterly down the 

 east side. The true bedding is in places replaced by a secondary vertical 

 structure. A coarse, rusty muscovite-biotite-gneiss, with graphite and tour- 

 maline in quite large prisms (the equivalent of the Washington gneiss far- 

 ther west), accompanies the limestone on either side, extending east to the 

 bend in the road and west to the house at the top of the hill. Just east of 

 this is a bed of typical Becket gneiss. In the yard of the ruined house the 

 mantle of the Becket gneiss is so nearly continuous that a boss of white 

 limestone a foot wide projects from the ground, and only a few feet on 

 either side the Becket gneiss dips away from it. 



Interest attaches to the fact that the Becket gneiss is so strongly meta- 

 morphosed as to form a quarry stone of first quality only in a narrow band 

 along either side of the limestone belt, as if the violent upthrust of the pre- 

 Cambrian rocks along this narrow axis had exerted an influence upon the 

 Cambrian gneisses for some distance outward, producing in them a marked 



