56 HENRY S. WASHINGTON 



The hyperitic variety is represented by two specimens from 

 the southwestern part of Salem Neck, which only differ from 

 Sears' type in being a little more coarsely crystalline, but much 

 less so than the hyperitic diorites to be described later. The 

 structure is somewhat ophitic, the feldspars being thick tabular, 

 and the ferromagnesian minerals frequently xenomorphic towards 

 them. At the same time these occupy bays and form inclusions 

 in the feldspars, so that the crystallization must have been to a 

 certain extent simultaneous. The chief peculiarity of the struc- 

 ture is the zonal growth of the biotite and hornblende about the 

 pyroxene, olivine, and magnetite. 



The feldspars are almost exclusively plagioclase, which is 

 usually fresh, and with rather thick twinning lamellae, whose 

 extinction angles correspond to a basic labradorite, about Ab t 

 An 3 . Only a few grains of alkali-feldspar could be seen, and 

 nothing which could be identified with nepheline. Olivine is 

 present in some quantity, as rather large grains, usually auto- 

 morphic though corroded. They are generally fresh, but some- 

 times partially serpentinized. A colorless or pale fawn-colored 

 augite is present which shows high extinction angles. A reddish- 

 brown barkevikitic hornblende is very abundant, showing the usual 

 pleochroism ; C = deep red-brown, b = deep red-brown, a = light 

 brownish yellow, C> t> > a. It seldom forms independent indi- 

 viduals, but nearly always occurs as a border about the pyroxene 

 and olivine. This border, which is usually of the nature of a 

 reaction rim between the pyroxene or olivine and the feldspar, 

 is highly irregular, often of great relative thickness, and in 

 many cases almost entirely replaces the pyroxene. A brown 

 biotite which is present in less amount also occasionally plays 

 the same role. Magnetite and ilmenite grains are abundant, and 

 about them is almost constantly found a hornblende rim when 

 they are included in pyroxene, while, if they are included in 

 feldspar, this is less common. Apatite is rare. 



An analysis was made of a specimen from Salem Neck which 

 was given me by Mr. Sears as representing his type. An analysis 

 of a similar specimen, made by M. Dittrich for Professor Rosen- 

 busch is given in II. 



