110 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



origin. It contains, however, bands several centimeters broad of dark- 

 green, matted, fibrous actinolite. 



Associated with this in another large bowlder is an entirely distinct 

 limestone, a white, coarse, granular calcite, all the grains showing with the 

 lens abundant twin striation, while the limestone mentioned above is 

 too fine-grained to allow its structure in this respect to be seen, and under 

 the microscope it is not twinned at all. It must be calcite, however, as it 

 eff'ervesces freely with cold acid. In the limestone now described a distinct 

 stratification is effected by the interposition of fibrous masses of emerald- 

 green actinolite upon the foliation planes, and in the midst of the granular 

 calcite fine grains of coccolite and magnetite occui-. 



12. '■'■Dolomite-serpentine, Granville.''' — XIII, No. 26, Massachusetts Sur- 

 vey Collection ; PI. II, fig. 2. This is a black serpentine, containing much 

 white to greenish, granular dolomite, and is identical with the bowlders 

 described above from near the cemetery in Grranville. Remnants of the 

 gray-green enstatite in every stage of change to phfestine appear, and prove, 

 under the microscope, identical with those described above, and the traces 

 of enstatite structure can also be distinctly seen in the completed serpentine. 



The most interesting change here is that of the dolomite into chrysotile, 

 many stages of the Eozoon structure being beautifully represented. 



The slide (PI. II, fig. 2.) shows a network of yellow serpentine, 

 amorphous in common light, running through the dolomite and generally 

 following the cleavage. The dolomite network appears where the car- 

 bonate has whollv disappeared. The dolomite fragments are surrounded by 

 a quite bi'oad, dark band, consisting of short, stout rods of the unchanged 

 dolomite whicli project into the serpentine. 



The dolomite shows exceptional absorption, and this dark band absorbs 

 and extinguishes with it. Outside this band the serpentine veins polarize 

 with wavy extinction and low colors, and show the most delicate fibrous 

 structure, with central suture. 



13. Enstatite-serpentine. — H. Cooley, Granville (PI. II, fig. 3). The 

 section cut parallel to the base of the large crystals of enstatite changed into 

 serpentine shows a series of bands which appear in pairs separated by a 

 narrow line of magnetite. These are the light bands seen in the figure, and 

 broad surfaces could have been selected where these bands were more closely 

 parallel tliaii in the one drawn. The drawing was made with crossed nicols, 



