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GEOLOGY OF OLD HAMPSHIEE COUNTY, MASS. 



50 rods wide, of a dull, dark-gray, slightly gi-eeuish amphibolite, thin-fissile 

 and highly porphyritic. It closely resembles the Guilford band in its wider 

 portion across Vermont, west of Brattleboro, where the latter is porphyritic. 

 The porphyritic spots are due to feldspar, which excludes the hornblende, 

 but is itself full of impurities, especially biotite. The latter is wanting in 

 the main mass. It lies near the western border of the Goshen schist and 

 passes through the railroad cut east of Charlemont station. The upper 

 amphibolite bed of the Hawley schist is at times porphyiitic, and I have 

 assumed that this Heath bed was a repetition of that upfolded through the 

 Goshen schist. The small content of lime and magnesia may be thought 

 to militate against this assignment and indicate a relationship to the Guil- 

 ford and Whately bands, which occur in the Goshen schist far to the east, 

 and this is perhaps the best assignment of tlie bed. 



An analysis of the rock has been made by Mr. L. G. Eakins, from a 

 specimen taken from near W. M. Sanford's: 



Analysis of Heath amphibolite. 



The white gneiss.— A single curious band of white, thick-bedded gneiss 

 runs down thi'ough the middle of the Hawley schist area. It passes through 

 the southwest comer of Halifax, Vermont, and can be well studied on the 

 high hill south of the road. It is a very prominent bed on the road going 



