242 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



well exposed in a section continued a mile east from the town farm, or east 

 from South Monson, past the liouse of T. K. Beckwith. 



After passing over the Monson gneiss and the araphibolite one comes 

 upon a band of gray, fine-grained, thin-fissile gneiss containing garnets, 

 which represents the whetstone-schist, but is so thin that it is not separately 

 represented upon the map. It contains a small amount of fibrolite in the 

 finest needles. 



Just above it is a dark, fine-grained mica-schist, full of small garnets 

 and spangled with transverse biotite that exactly resembles the Conway 

 mica-schist, except that it contains fibrolite. 



On the next road south, in the roadside by S. Blodgett's, the rock is a 

 -•^ery striking one. It was originally an arenaceous band in the mica-schist, 

 like the whetstone layers in the Conway mica-schist on the west of the river. 

 It has now assumed the chocolate-brown color of the rest of the rock, and 

 is full of fibrolite needles that wind with an excellent imitation of a fluidal 

 sti'ucture around porphyritic masses of feldspar or garnet, which reach a 

 diameter of 25-30"™, and very closely imitate pebbles. They are well 

 rounded, but consist in each ease of a single crystal. 



The feldspar is a perfectly fresh and slightly opalescent moonstone, 

 regularly penetrated by blades of plagioclase so exceedingly fine that, 

 except with thin plates and very high powers, it seems to be an orthoclase 

 of ideal purity. These rounded masses are bounded by a sugary, granular 

 border of white feldspar, clearly produced by the crushing of the central 

 mass, and I have nowhere seen the cataclase structure more beautifully 

 developed. 



The average rock of this band across Monson is a rusty, chocolate- 

 brown biotite-schist, everywhere abundantly fibrolitic and graphitic, and 

 very generally carrying garnets. Occasionally it is changed into a gneiss, 

 as described above, by the development of the porphyritic feldspars, but 

 this seems so plainly a modification of the mica-schist during folding, by 

 the warping open of cavities which became filled with feldspar, that I have 

 not separated it upon the map. 



On the east of the mica-schist only traces of amphibolite could be 

 found along the line of separation of the schist and the band of gneiss 

 still farther east, and this could not be given on the maj) without great 

 exaggeration. 



