F. H. Lahee — Metamorphism and Geological Structure. 459 



As we have explained in Part I, the strikes of the beds 

 in the southwestern portion of the Basin are nearly north-son th 

 and the dips are commonly steep eastward (fig. 1). The 

 attitude of the schistosity is usually similar. These structures 

 (either or both) had a general directional influence upon the 

 intrnsives, and this influence was more efficient southward. 

 Thus, in the Watson's Pier district, the dikes, which are pre- 

 vailingly of large size, usually trend along north-south lines. 

 On the other hand, in the Bonnet exposures,* large dikes are 



Fig. 5. Fig. 6. 



Fig. 5. Pegmatite dikes in schist. Note the distortion of the schistosity 

 against the dikes. (Southern end of Boston Neck.) 



Fig. 6. Pegmatite dike cutting Carboniferous sehist and having inclu- 

 sions of the same. (Figs. 6 to 12 are of features seen on the Bonnet.) 



few and, when present, may cut the strata obliquely or may 

 bend sharply from a nearly north-south course and, crossing 

 the beds nearly perpendicular to the strikes, disappear under 

 the waters of the Bay or landward beneath the soil. 



Small dikes and apophyses are more numerous on the Bon- 

 net than on Boston Neck. In the former place many of them 

 show absolutely no dependence upon structures in the country 

 rock. A few have been seen to extend into joints of an east- 

 west set. When they are approximately or quite parallel to the 

 cleavage, they may be relatively long and narrow and of pretty 

 uniform thickness (fig. 4) ; where they cross the cleavage, they 

 are shorter, thicker, bunchy or highly irregular in shape, or 

 are convoluted (see figs. 5-11). Yet that this is not always 

 true is proved by the straightness of such stringers as the 

 middle third of the small apophysis on the left in fig. 11. 

 Sometimes pinching seems to have brought about a separation 

 of the dike (fig. 10). In this case, however, it should be noted 

 that the two ends do not lie in the same cleavage plane. In spite 



* The strata of the Bonnet have a well developed cleavage which strikes a 

 little east of north and has an average dip of 60° E. Differences of texture, 

 where visible in these rocks, prove that the bedding has a like attitude. 



