GENERAL STRUCTURE AND CORRELATION. 15 



dinally through an anticline; a few hundred feet west of the river there is 

 a massive anticline of marble exposed in large quarries; the eastern end 

 dips toward the river, but a sharp anticlinal fold, slightly overturned to the 

 west, brings the strata, up near the west hank of the stream, in interstrati- 

 lied beds of limestone and schist. The arch springs over the river, and its 

 easterly dipping limb forms a high cliff on the eastern bank. In this eastern 

 limb the limestone is represented by calcareous siliceous-micaceous schists 

 and very impure limestones. The whole arch is exposed near by, in a cliff 

 in the bend of the river (see Fig. 4). 



This is the most eastern exposure of limestone, and there can be no 

 doubt that we are here in the zone of lateral transition between the condi- 

 tions that produced in the same horizon the Stockbridge limestone and part 

 of the Hoosac schist. Again, along the north base of the Dalton hills, in 



bb. 



<5oo feet 



Fig. 4.— Anticlinal arch across Hoosic river between North Adams and Briggsville, 

 in the zone of lateral transition between Stockbridge limestone anil Hoosac schist; 

 a. limestone more or less micaceous and siliceous: b, calcareous ami siliceous -< hie! 

 with thin layers of limestone; aa, interstratified siliceous and micaceous limestone. 

 calcareous quartzite and mica-schist; bb, less calcareous garnetiferoua schist. 



Cheshire. Mr. Wolff found a schist consisting of calcite, mica, quartz and 

 simple twinned albite, which, from its position and nature, undoubtedly 

 represents this zone of lateral transition from limestone to schist. 



If the reader will turn to Plate n he will see that the Stockbridge 

 limestone sends ;i broad rectangular bay southeast in Cheshire to conform 

 to the embayed topography of the Dalton- Windsor hills. In the middle of 

 this embayment he will observe a detached area of Berkshire schist of an 

 irregular shape, suggesting a long-eared rabbit. There is no question as to 

 the continuity of the schist over the area as represented. The long rabbit- 

 ear-like area lies upon the limestone in a synclinal trough. The structure 

 of this area is not simple: it is that of a small synclinorium, the axes of the 

 north-south running folds pitching toward the center, and the folds at the 

 northern end being more or less overturned to the west in conformity with 



