GEOLOGY OF MONADNOCK MOUNTAIN 3 



ridge, and also in the western peak of the mountain, these 

 prisms are now largely, if not entirely, made up of fine, glassy,, 

 colorless or white fibers of fibrolite. In the northern part of the 

 eastern ridge, and in other parts of the mountain in limited 

 areas, the andalusite crystals have changed to masses of white, 

 pearly sericite scales. In the weathering these sericite masses 



Fig. 2. — Surface of Andalusite mica schist. 



are removed more rapidly than is the inclosing rock, producing 

 long narrow cavities on weathered surfaces. Where the end of 

 the sericite mass is exposed, the weathering is more rapid in the 

 center, producing a cavity bordered by a sericite shell. 



In the southern part of the mountain the schist becomes, by 

 alternating areas, a fibrolite schist, the fibrolite being original ; 

 but even within this fibrolitic area appear small areas where 

 the rock originally contained andalusites. It is impossible to 

 draw a line correctly separating this schist into two parts, so 



