90 NEW YORK STATE MUSEUM 



further significance than to denote the original lack of that 

 structure. 



The rock is composed of quartz and feldspar with varying 

 amounts of biotite, augite, bronzite and hornblende, and with 

 magnetite, apatite, zircon, and a little occasional titanite as acces- 

 sories. 



The quartz content ranges from 5^ to 25^. It is evidently all 

 recrystallized and commonly of coarser grain than the other 

 minerals, though never prominently of the leaf type. Its increase 

 in amount is accompanied by diminution of the dark silicate con- 

 tent, specially of the augite and bronzite. 



Feldspar makes from 65^ to 85^ of the rock. It is mostly of 

 faintly moirt? appearance, seldom well marked microperthite, and 

 is presumably anorthoclase. But some oligoclase is always pres- 

 ent as well, usually in small amount, but rising to as high as 25^ 

 of all feldspar present. The mineral is usually in equidimen- 

 sional grains, constitviting a fine mosaic, and, except for an occa- 

 sional larger individual with traces of cataclastic structure, 

 seems to have been wholly recrystallized. The larger fragments 

 are usually of well marked microperthite. 



Biotite is the most constant of the dark silicates, occurring in 

 nearly all varieties of the rock, and being practically the only 

 one to persist in the more acid varieties. Bronzite is perhaps 

 next in abundance. Sometimes all four (bronzite, augite, horn- 

 blende and biotite) are present, and then biotite plays a subordi- 

 nate role. Including magnetite these minerals never make more 

 than 15^ of the rock, and in the quartzose members may fall 

 below 5^. 



Rocks at the Salisbury iron mine. Ore. The thin section of the 

 purest ore which the writer could find on the dumps shows the 

 presence of many inclusions of other minerals, though indicating 

 that these are not present to the amount of more than 15^ to 20^, 

 and hence that the ore is rich, though there is nothing to show 

 how large a proportion has this character. Professor E. W. Mor- 

 ley was so good as to make a test of the ore for titanium, his 



