F. II lahee — Metamorphism and Geological Structure. 465 



Again, we have shown that, in the Bonnet-Boston Neck 

 region, stratification appears to coincide with the planes of 

 schistosity. The Carboniferous rocks of this district are of 

 comparatively uniform texture. Conglomerate schists are fine- 

 grained and are rare, and very fine pelitic schists are not com- 

 mon. The bulk of the sediments are sandstone schists which 

 range from coarse to fine. We might conclude, then, that the 

 stratification, per se, would not have afforded easy access to an 

 intrusion — certainly by no means as easy as if the sedimentary 

 series consisted of rapidly alternating textures. 



On the other hand, since schistosity is well developed, it 

 would seem to have offered relatively little resistance to the 

 injection of magma along its planes. 



These facts being admitted, we may assume provisionally 

 that those dikes which trend parallel to the schistosity and 

 bedding were guided more efficiently by the schistosity than 

 by the bedding. 



Northward and eastward the quartz veins are best developed 

 in pelitic and coaly rocks, that is, in rocks of fine grain. In a 

 large sense, then, these veins may be said to be related to the 

 stratification ; but they occur in huge masses which cut promis- 

 cuously across the finer laminse of bedding and cleavage 

 alike, and are, therefore, not immediately dependent upon 

 either structure. 



The intimate relations between the pegmatite dikes and the 

 schistosity of the Carboniferous sediments were described 

 above (p. 457 et seq.). Among the features there mentioned, 

 the conspicuous lack of dependence of the intrusions upon the 

 direction of the schistosity, their occurrence sometimes in 

 series of lenticular bunches or in irregular masses, which seem 

 to have been squeezed apart, and their frequently tortuous 

 shape, are strongly suggestive of their having been injected 

 before the period of deformation and metamorphism, and of 

 their having been subsequently folded together with the sedi- 

 ments. But against this supposition, the following objections 

 may be raised : (1) The internal structure of the dikes reveals 

 little or no crushing. (2) Inclusions have schistosity which is 

 practically identical with that of the country rock in respect to 

 degree, nature, and direction. (3) Loops of pegmatite, which 

 surround such inclusions, prove that all curves of these dikes 

 could not have been parallel to the bedding. (4) In many 

 cases the loops are of a type difficult to explain if injection 

 preceded folding. (4) In the midst of an area containing 

 numerous, often highly tortuous dikes, perfectly or nearly 

 straight apophyses sometimes extend for considerable distances. 

 (6) The method in which the cleavage abuts against the dikes, 

 either by fanning out (fig. 12) or with minute local crumpling 



