5IO NEW YORK STATE MUSEUM 



As usual some uncertainties have a vitiating effect on the calcula- 

 tion. The pyroxene may, or may not be like the one analyzed. 

 If not the lime-magnesia ratio would be altered, though the change 

 would be slight. Most of the feldspar is twinned, though 15% lacks 

 this feature. This has been calculated as orthoclase though it 

 may not be. The remainder shows a maximum extinction of 16 . 

 This is the angle for both albite and andesin (Ab 3 An 2 ) but this is 

 held with reasonable certainty to be the latter since Becke's method 

 shows it to have the same refractive index as the quartz. Except 

 for a possible slight increase in lime and corresponding decrease In 

 magnesia therefore this must give 3, very close approximation to 

 the actual composition of the rock. It harmonizes well with the 

 preceding analyses and again indicates a somewhat impure sand- 

 stone, a little more aluminous and a little less calcareous than 

 they. 



Igneous rocks. Granite. No analyses of the Adirondack gran- 

 ites have been published, so far as the writer is aware. The Morris 

 granite is of a distinct and simple type, with definitely established 

 age relations to the other intrusives, and an accurate analysis of it 

 seemed highly desirable. It is mainly a quartz-microperthite rock, 

 with accessory plagioclase, hornblende (usually chloritized) , mag- 

 netite, titanite and zircon, and lends itself readily to microscopic 

 analysis. Since however the character of the feldspar can not be 

 precisely determined microscopically an analysis was necessary to 

 establish this. The hornblende has, been thoroughly altered to 



Mode of Morris granite, fine grained type (15-A-3) 



Units 

 Units measured Sp. Gr. by weight % weight 



Quartz 996x2.65 = 2639 = 34-57 



Microperthite 1804x2.6 = 4690 = 61.74 



Plagioclase : . . 20x2.63 = 153 = 2.01 



Hornblende 27x3.2 = 86= 1.13 



Magnetite 5x5.25 == 26 — 0.34 



Zircon 3 x 4 • 5 = I ?> = ol8 



Titanite 1x3.5 = 3 = ° - °3 



Total 2856 7610 too. 00 



chlorite and small flecks of this mineral are frequent in the feldspar, 

 and are too small to measure accurately, so that the hornblende 

 should more properly read " chlorite " and its amount is certainty 



