15 



changes at nearly every rod. One important fact should be noted 

 here, viz., nowhere in this region does the Naugus-Head 

 series appear to be cut by eruptives belonging to another for- 

 mation ; for all the exotic rocks of this group may be easily re- 

 ferred to, or shown to be derived from its stratified members. 

 The stratified rocks occur chiefly in Marblehead, and on the 

 Beverly shore west of Curtis Point. In Marblehead the strike 

 is E.— W., with a vertical dip; while on the Beverly shore 

 the strike varies from N.— S. to N.E.-S.W., and the dip 

 is thirty degrees to vertical to the N.W. The average strike 

 of the whole system is N. E.-S.W. More or less distinct 

 bedding has also been observed on the north side of Great 

 Misery, at several points on Salem Neck, on Coney Island, and 

 at one point on the north-east shore of Nahant. 



The rocks of this series are composed chiefly of feldspar and 

 pyroxene. These minerals occur mixed in very various pro- 

 portions. Perhaps the most characteristic rock is one composed 

 almost entirely of feldspar, containing little pyroxenic or 

 hornblendic material, and frequently destitute of it. It is 

 usually coarsely crystalline, this variety prodominating along 

 the Beverly shore east of Curtis Point ; and the crystallization 

 is sometimes extremely coarse, as, notably, on the Beverly 

 shore, near the western end of West Beach, and in Marble- 

 head, especially about Dolliber's Point. At the former locality 

 the rock is evidently exotic, and some of the feldspar crystals 

 are of immense size, ranging from three to six inches in length, 

 and one to two inches in breadth ; but at Dolliber's Point it is 

 distinctly bedded, and is interstratified with fine-grained pyrox- 

 enic rocks. Another, but less abundant, variety, is fine-grained, 

 presenting a very uniform texture and appearance, and ap- 

 proaching the compactness of felsite. This occurs at many 

 points, but is most largely developed on Baker's Island, which 

 is principally formed of it. A dark, heavy, usually coarse- 

 grained diabase or norite, varying greatly in composition, and 

 frequently occurring as a nearly pure pyroxene rock, is the most 

 abundant rock of this series. It is the prevailing rock on 



