MINEUALOGICAL NOTES. 149 



magma at the time of cooling and crystallization. Excess 

 of silica produced orthoclase, microline and albite ; de- 

 crease in silica and increase in potash produce anortho- 

 clase, and lime plagioclase. 



In some places, noticeably in outcrops on the Beverly 

 shore at Curtis' point, this rock becomes distinctly a horn- 

 blende-zircon-syenite. Here the feldspars are microper- 

 thitic intergrowths of albite and plagioclase with a large 

 proportion of magnetite. Still farther to the eastward 

 along the coast, at Gale's point on the Manchester shore, 

 occur veins of this rock, from a few inches to two feet in 

 width, which might with perfect propriety be described as 

 segirine-syenite for these veins are completely tilled with 

 acicular segirine crystals, some of which are two inches 

 long and one-sixteenth of an inch wide. The feldspar in 

 this rock has the optical character of anorthoclase. 



The porphyritic-syenite Keratophyre of Marblehead har- 

 bor and the Beverly shore is again seen as a dyke mass 

 in the granite at a road cutting near Pride's station, Bev- 

 erly. This dyke is fifteen feet wide and is exposed for a 

 distance of fifty feet. In this rock the anorthoclase phen- 

 ocrysts are completely honeycombed with inclusions of 

 glass, while the base is composed of the same kaolinized 

 and chloritic mass with minute lath-shaped feldspars inter- 

 spersed through it, as in the Keratophyre at Marblehead. 

 There is, again, a good outcrop of apparently the same 

 rock in a railroad cutting between Newton and Newton 

 junction, New Hampshire. Thin sections which I have 

 made from this outcrop, studied with the polarizing micro- 

 scope, have all of the optical characters of the Kerato- 

 phyre from Marblehead harbor. This shows that Kerato- 

 phyre (porphyritic-syenite) is not confined to the small 

 area previously described in a paper by me printed in the 



