42 GEOLOGY OF OLD HAMPSHIEE COUNTY, MASS. 



aud the gneiss then extends continuously across the State to Northfield, 

 where it is partly covered by newer rocks before reaching- the State line. 

 The eastern band runs north to Orange, where it disappears completely 

 within the limits of Massachusetts. 



On returning to the study of the Monson gneisses, after long experience 

 with the change of the Cambrian conglomerates into the white gneisses in 

 the Berkshire Hills, the traces of the same change struck me in the stretched 

 gneisses of Monson and Pelham. The traces of pebbles may now and then 

 be clearly seen, and I present a reproduction of a photograph of the north- 

 east corner of Walker Hall, one of the buildings of Amherst College, which 

 shows this clearly (PI. I, p. 64). The rock is from Monson, and in 1890 

 a great wall of conglomerate was exposed in the quarry just north of the 

 trap dike, but it was all quarried away in 1892. In many cases the flat 

 patches of lighter color and of long elliptical shape which appear on the 

 cleaved foliation faces of the gneiss seem to be the remains of pebbles 

 wholly flattened out into films, as was suggested by President Hitchcock 

 in his remarkable investigation of distorted pebbles.^ 



THE PELHAM AND WILBRAHAM AREA. 

 THE GNEISS. 



The broad anticline of this area enters the towns of Northfield and 

 Warwick from New Hampshire, and though its surface is at first covered in 

 part by isolated areas of newer rocks, it soon expands to a greater width 

 than any other gneiss in the counties, and maintains this width nearly across 

 the State, interrupted by the protrusion of the Belchertown tonalite. 



It is in Northfield a fine quan-y stone, especially marked on foliation 

 faces by small squarish blotches of jet-black hornblende, and it continues 

 to be good quarry stone in large part clear across the State. It dift'ers 

 cm-iously from the other areas in that it is, across the central portion of the 

 State, a broad anticline with all its central portions almost horizontal and 

 at the edges bending down quite sharply beneath the newer rocks. A 

 fmlher distinction of this area is found in the presence of a great bed of an 

 actinolite-quartzite, which will be specially described, and in the presence 

 of three great intrusions of an olivine-enstatite rock, which, with its complex 

 contact phenomena, will be also the subject of a separate chapter. 



• Geology of Vermont, Vol. I. 1861, p. 28. 



