F. H. Lahee — Metamorj>hism and Geological Structure. 371 



30 



Moderate 





B 





Moderate 



36 



Considerable 







e 



Considerable 



37 



Low 







A 



Moderate 



38 



Moderate 



.. 



B 





Considerable 



40 



u 



C 



B 



B 



u 



41 



cc 







B 



Moderate 



44 



Considerable 



"c 







High 



49 



Variable 





C 



A 



Variable 



50 



Moderate 



.. 



B 



_. 



Moderate 



This table indicates a close dependence of the intensity of 

 metamorphism upon the degree of contortion. Whether the 

 outcrops are situated on the limbs or in the axial regions of 

 major folds appears to make no difference. 



Relations of the Schistosity to the Bedding. 



In a majority of the outcrops examined the schistosity was 

 nearly, if not quite, parallel to the stratification.* However, 

 while this is true of the coarser rocks, it does not so often hold 

 for the pelites. Very notable exceptions are frequent in the 

 greenish schists of southern Conanicut Island. 



Linear schistosity, when well developed, may trend parallel 

 to the strike of the beds, or parallel to their dip, or in some 

 other direction. Most often, perhaps, it coincides with the 

 strike. This relation is not commonly evident in the psammitic 

 and pelitic rocks on account of their fine texture ; but in the 

 conglomerates it is easily discerned in the attitude of the 

 elongated pebbles. f The data obtained in the field work 

 prove that parallelism with dip or strike is generally in regions 

 where the strikes are uniform (western coast belt, southern 

 Aqnidneck Island), and that departures from this relation are 



* Collie (op. cit., p. 213) described this for Conanicut Island, and inferred 

 that the " schistosity was developed pari passu with the tilting of the rocks, 

 and that both processes were due to dynamic pressure." 



f The lengths of distorted pebhles in metamorphosed conglomerates have 

 been recorded as parallel to the strike of the beds, by H. H. Reusch (Die 

 Fossilien Fuhrenden Krystallinischen Schiefer von Bergen in Norwegen. 

 German translation by R. Baldauf . Leipzig, 1883. Pp. 52-53) ; Ed. Hitch- 

 cock (Final Report on the Geology of Mass. Amherst and Northampton, 

 1841. P. 535; and also, On the Conversion of certain Conglomerates, etc., 

 this Journal (2), xxxi, 372. 1861. P. 384) ; and W. O. Crosby (Contribu- 

 tions to the Geology of Eastern Mass., Bos. Soc. Nat. His., Occas. Papers, 

 1880. Pp. 148-149). On the other hand, the case in which the pebbles lie 

 lengthwise parallel to the dip has been described by Ed. Hitchcock (On the 

 Conversion of certain Conglomerates, etc. Loc. cit., p. 380); C. H. Hitchcock 

 (General Report upon the Geology of Maine ; in the Sixth Ann. Rept. of the 

 Secretary of the Maine Board of Agriculture, 1861. P. 182); and W. P. 

 Blake (The Plasticity of Pebbles and Rocks : Proc. Am. Assoc. Adv. Sci., 

 xviii, p. 199. 1869. P. 201). These differences are caused, no doubt, by 

 the diversity of orientation of the maximum, intermediate, and minimum 

 values of complex forces during deformation. 



