168 W. H. HOBBS METAMORBHISM OF BERKSHIRE SCHISTS. 



the limestone. The rocks here described occur in portions of the town- 

 ships of Egremont, Sheffield and Mount Washington, in Massachusetts, 

 and of Canaan and Salisbury, in Connecticut. They have been studied 

 areally and structurally in the field and petrographically in the labora- 

 tory. The full report of the investigation will appear elsewhere.* 



The area includes three beds of schist separated by beds of limestone, 

 besides the thin layers of the former which are sometimes found within 

 the limestones near the contact. The lowest of these schist beds is asso- 

 ciated with quartzite and gneiss, and is more lacking in uniformity of 

 character than the others. It incloses numerous veins of coarse pegma- 

 tite and is specially rich in tourmaline, though this mineral is also found 

 in the two other horizons. 



The next younger schist is separated from the one just mentioned by 

 a dolomite, which is always very crystalline, and at many localities con- 

 tains white pyroxene, tremolite or phlogopite. It moreover contains 

 layers of graphitic rock and of canaanite.f The schist horizon itself is 

 quite variable in character, but is frequently distinguished by the occur- 

 rence of macroscopic garnets and staurolite. 



The upper schist bed is separated from the last mentioned by a lime- 

 stone in which neither sahlite, tremolite nor canaanite has been found. 

 The schist itself is free from the macroscopic garnets and staurolite 

 characteristic of the central bed. In common with both the other beds 

 it contains porphyrinic crystals of feldspar, but here they seem more 

 generally to have glistening cleavage surfaces. Especially in the Mount 

 Washington area this bed shows facies that are quite sericitic or chloritic, 

 the latter with magnetite often in octahedra as big as a pea. Ottre- 

 lite, though not restricted to this horizon, is more frequently found here 

 than in either of the others. Though the rocks of the three non-calcare- 

 ous beds have a preponderance of feldspar, they are structurally schists 

 and they are so designated, as it is convenient to distinguish them from 

 typical gneisses in adjacent territory. Notwithstanding characteristic 

 differences can be pointed out, serving to distinguish the three beds when 

 regarded as units, individual hand specimens from each often show re- 

 semblances more striking, so that it is generally impossible to refer a 

 specimen to a definite bed on the basis of petrographic character only. 



Evidences of orographic Disturbances. — Typically metamorphie minerals 

 abound in all beds, but especially in the central schist bed and the dolo- 

 mite underlying it. The beds have been thrown into sharp folds, most 

 frequently reversed, with resulting shear planes and secondary foliation 

 at many localities. 



*The work here referred to forms part of an investigation conducted by Professor Raphael 

 Pumpelly for the United States Geological Survey, 

 t American Geologist, vol. xv, 1892, p. 45. 



