32 GEOLOGY OF OLD HAMrSHIKE COUNTY, MASS. 



bddv during the later folding of the newer gneiss. This is well seen along 

 the railroad from above Becket to Bancroft station, in Middletield, where 

 one passes four principal anticlines with their intervening syuclines, as well 

 as nianv subordinate flexures, all pitching southward. 



DESCRIPTION OF THE ROCK. 



The prevailing rock is a rather tine-grained biotite-gneiss, always in 

 some degree friable and breaking crisply, and without the extremel}- firm 

 texture of the older series. Sometimes it is, while seemingly quite fresh, 

 so softly saccharoidal as to crumble under the pressure of the fingers, and 

 ao-ain so brittle that a blow of the hammer will punch a square hole in the 

 middle <>t a thin slab without cracking it. It shows clear gray shades, 

 dependent for their depth upon the amoixnt of the biotite present, which is 

 in clear black to dark-brown scales, both the feldspar and the quartz being 

 colorless, limpid, and much fissured. It contains very few accessory min- 

 erals and only small and luiimportant veins of coarse granite. It varies 

 from a very thin-fissile rock — "scaly," the quarrymen call it — to a fine- 

 grained granitoid-gneiss, furnishing a quarry stone of the first quality, equal 

 to anything in New England for all kinds of monumental work. 



It is best exposed for study along the Boston and Albau}- Railnjad 

 below Becket station, and a brief description of this section will give a 

 o-ood view of the range of variation in the rock, although it must be noted 

 that the section is not taken at right angles to the dip, and that it contains 

 y(jveral repetitions of the same strata, as the folds around the older gneiss 

 are traversed. 



From Becket station east to the Middlefield line the older, rusty, pre- 

 Cambrian gneiss with small segregated granite veins continues, passing thi-ee 

 bridges, and changes here immediately into a light-colored, fine-grained 

 granitoid gneiss, which continues a long distance to the next (fourth) 

 bridge, becoming gradually bedded. The change takes place across the 

 strike, and the rock dips 70° E. ; the passage Ijeing apparently from lower 

 to higher beds. A little farther, east of the next (fifth) bridge, and thus 

 still higher up, a stratum of thin and wavy bedded muscovite-gneiss occurs, 

 which is quite exceptional so far east in this series. Then for a long dis- 

 tance a "scaly" biotite-gneiss, often subporphyritic and rusting from the 

 abundance of the pyrite which is disseminated through it, runs on in great 



