GEOLOGY OF THE HAYSTACK STOCK 217 



The norm of E, calculated from the analysis, is given in column I 

 of the following table, the mode in column II. 



I. Norm II. Mode 



Quartz 1.56 Quartz 3.7 



Orthoclase 16.12 Orthoclase 13.2 



Albite 28.82 Albite 26.5 



Anorthite 20 . 29 Anorthite 18.9 



Hypersthene 13-88 Pyroxene 28 . 8 



Diopside 11 . 22 Olivine and Serpentine 0.3 



Magnetite 4.18 Biotite 3.1 



Ilmenite i . 98 Magnetite and Ilmenite 4.8 



Apatite i . 01 Apatite 0.7 



Water o . 97 t^ *. 1 



^' 1 otal 100 . o 



Total 100 . 03 



Variety E is among the most basic of the Haystack rocks, and, 

 according to the quantitative system of classification, is a shoshonose. 

 It is closely similar to a diorite from Rock Creek, Crazy Moimtains, 

 Mont., described by Mr. J. E. Wolff,^ and to a large number of 

 shoshonites from the Yellowstone National Park, described by Mr. 

 Iddings.^ It is a little lower in potash than these rocks and richer 

 in the ferromagnesian constituents. 



VARIETY F. HESSOSE: OLIVINE-GABBRO 



This variety is a dark gray, coarsely crystalline olivine-gabbro which 

 occurs near the center of the stock. The specimen was taken near 

 the base of the cliff southwest of Mud Lake. It is the most basic 

 variety of the stock and is composed of feldspar, pyroxene, biotite, 

 and olivine, the ferromagnesian minerals constituting about two-fifths 

 of the whole. 



Under the microscope the texture of the rock is hypidiomorphic 

 granular, and the following minerals, named in relative order of 

 abundance, are present: labradorite, augite, hypersthene, olivine, 

 orthoclase, magnetite, biotite, and apatite. Labradorite occurs as 

 crystals about i™^ long, approaching idiomorphism, and is twinned 

 according to albite and carlsbad laws. Orthoclase, containing a 

 little graphic quartz, is present as irregular bodies, filling interstices 

 between other minerals. The pyroxenes occur as anhedra from J 



1 Bulletin No. 148, U. S. Geological Survey, p. 144. 



2 Journal of Geology, Vol. Ill, and Bulletin No. 168, U. S. Geological Survey. 



