Il6 HENRY S. WASHINGTON 



pleochroic in light tints of blue-green and yellow-green, and 

 with an extinction angle of 15 , partly in large, stout pheno- 

 crysts, but mostly as small, irregular grains, with small, stout 

 flakes of a peculiar light brownish-gray biotite, embedded in 

 microperthitic feldspar, generally in anhedra, but occasionally 

 showing roughly tabular forms. Neither aegirite nor the nor- 

 mal blue hornblende is to be seen, nor was any quartz found. 



A very pretty solvsbergite forms Dike 55, which cuts the 

 granite at the pier of the Hawthorne Inn, East Gloucester. The 

 rock is aphanitic and chiefly a dull gray, but is mottled with 

 streaks of white or greenish-gray, which run parallel to the walls. 

 Under the microscope the only phenocrysts visible are a few 

 sharply automorphic ones of alkali-feldspar, which are composed 

 of orthoclase and albite, not arranged microperthitically, but 

 forming aggregates of small granular anhedra. This structure 

 seems to be due to secondary processes, as the rock is not quite 

 fresh, and the sharp crystal outlines of the aggregates show that 

 they were originally well-defined crystals. The groundmass is 

 composed of a finely granular alkali-feldspar, possibly with a 

 little quartz, thickly sprinkled with small blue or green needles. 

 Most of these are of bluish-gray glaucophane, and are of two 

 sizes. The smallest, usually less than .01 mm in length, tend to 

 accumulate in rounded patches or streaks, surrounded by clearer 

 feldspar carrying sparsely scattered, larger needles. Other 

 streaks occur in the sections, corresponding to the pale streaks 

 seen in the hand specimen, which are of feldspar carrying pale 

 green aegirite needles and grains, with little, if any, glaucophane. 

 In one place the orthoclase and albite are intergrown radially, 

 forming sphaerocrystals which give a black cross between crossed 

 nicols. 



Another solvsbergite, the specimen of which I owe to the 

 kindness of Mr. Sears, occurs as a dike at West Cove, Coney 

 Island, in Salem Harbor. This has been described by Rosen- 

 busch, who calls it a bostonite-porphyry. 1 To a certain extent, 



1 ROSENBUSCH, Mikr. Phys., Vol. II, p. 425; also Elemente der Gesteinslehre, 1898, 

 p. 198, where it is called " bostonitic alkali-syenite-porphyry." 



