IGNEOUS ROCKS 453 



west of the West Wrentham station. The rock is dark gray in color and 

 consists essentially of plagioclase feldspar, abundant biotite, and subor- 

 dinate microcline and quartz. It is fine in grain and somewhat schistose 

 in texture. In thin-section the plagioclase is apparently an oligoclase 

 and is more or less automorphic in habit. Microcline, with a small 

 amount of plagioclase intergrown with it, is distinctly subordinate to the 

 oligoclase in amount. The quartz is crushed and is less abundant than 

 the microcline. Biotite is abundant, mostly in the form of small flakes 

 unevenly disseminated through the rock. Grains of iron oxide, probably 

 titaniferous, since they are often margined with leucoxenic material, and 

 apatite are accessory, while epidote and sericite are abundant secondary 

 products. The last two, together with much of the biotite, are scattered 

 through the plagioclase crystals. The rock has evidently been subjected 

 to considerable metamorphism. 



The quartz diorite of this locality is cut by many small dikes of a fine 

 biotite granite of the Milford type, and these appear to resemble very 

 closely the fine granite which occurs in small amount northwest of Grants 

 Mills near the State line. 



Another mass of quartz diorite outcrops prominently on the west side 

 of the road leading from Grants Mills to Diamond Hill. A little farther 

 west this is replaced by large ledges of the Grants Mills granite, which 

 here seems to grade distinctly toward the diorite in mineral composition, 

 but the contact or transition, whichever it is, between these two is unfor- 

 tunately not exposed. A similar quartz diorite is found in the fields 

 southeast of Grants Mills and also in the fields west of the quarry on 

 Diamond Hill. 



The quartz diorite from this Grants-Mills-Diamond Hill locality is a 

 rather dark greenish gray rock, fine in grain and quite strongly sheared. 

 It consists of heavily saussuritized oligoclase or andesine feldspar (filled 

 with zoisite, etcetera), abundant pale green hornblende, subordinate 

 quartz, and little or no microcline. The accessories are magnetite or 

 ilmenite, zircon, and apatite. Some leucoxene has developed. The third 

 locality is south of Hunting Hill, in the southern part of the field. The 

 quartz diorite is here a dark gray-green rock of about the same grain as 

 that west of West Wrentham. The plagioclase is andesine and is very 

 heavily altered. Much chlorite is present, probably secondary after 

 biotite. The southern extension of this mass has not been traced. 



The Albion quartz diorite occurs apparently as a small dike cutting 

 Cumberland quartzite. The outcrop is situated a few feet west of the 

 railroad track, near the first quartzite outcrop north of Albion. The 

 rock is very dark gray in color and shows hornblende crystals. In thin- 



