GEOLOGY OF THE HAYSTACK STOCK 



219 



Variety F is the most basic of the Haystack rocks, and, according to 

 the quantitative classification, is liessose. In composition it resembles 

 an olivine-basalt from Franklin Hill, Plumas County, California, 

 described by Mr. H. W. Turner,^ an augite-diorite from Stony Moun- 

 tain, Ouray County, Colorado, described by Dr. Whitman Cross, ^ and a 

 basalt from Prospect Peak, Yellowstone National Park, described by 

 Mr. Iddings.3 



Chemical variation of varieties. — The analyses of the six varieties are 

 given in the table below. The combining molecules of the rocks which 



ANALYSIS OF TYPES OF HAYSTACK STOCK. GEO. STEIGER, ANALYST 



A 



B 



C 



D 



SiO^ 



AI2O3.... 



FeO 



MgO 



CaO 



Na^O. . . . 



K,0 



H,0-... 

 H,0 + ... 



TiOa 



CO. 



P.Os 



NiO 



MnO 



BaO 



SrO 



Total 



65.06 



14.71 



2.82 



1-31 



2.48 



3-43 

 3.86 



3-48 

 0.31 

 1 .10 

 0.61 



0.18 



0.05 



64.09 



16. 20 



2.61 



2.40 



2.06 



4-51 

 3.88 

 2.51 

 0.22 

 0.44 

 0.49 



0.24 



0.09 

 o.is 

 0.03 



57-98 

 17.01 



3-34 

 3-34 

 2.74 



7-35 

 3-92 

 2.02 

 o. 14 

 0.49 

 0.90 



0-43 

 trace 

 o. 12 

 0.06 

 0.02 



54-84 

 16.41 



3-63 

 4-54 

 4.71 

 6.64 



3-27 

 2.83 



0-34 

 0-93 

 0.99 



0-35 



o. 12 



0.05 



54-09 



16.00 



2.92 



7-37 

 3-38 

 2.67 

 o. 20 

 0.77 

 0.99 



0-35 



0-15 

 o. 10 

 0.06 



47-87 

 16.34 



3-59 

 7.17 

 7.80 



2-43 

 0.92 

 0.28 



I. 25 



1 .02 



0.44 



0.41 

 0.02 

 0.14 



0.03 



99.68 



99.92 



99.86 



99-65 



99.78 



100.04 



have been analyzed, arranged according to the increase of silica, 

 are shown in Fig. 2. Silica is platted as the abscissa and 798 com- 

 bining molecules are taken as an initial point. The alkalies, alkali 

 earths, alumina, and iron are taken as ordinates. The diagram 

 shows graphically the irregularity in the variation of the oxides. 

 Alumina shows little variation, about the same quantity being present 

 in all analyses. Its total range of variation is but 23 molecules. 

 The granodiorite A is least aluminous. None of the oxides vary 

 directly or inversely with alumina, which is higher than any of the 



1 Seventeenth Annual Report, U. S. Geological Survey, Part I, p. 734. 



2 Bulletin No. 148, U. S. Geological Survey, p. 180. 



3 Mon. XXXII, U. S. Geological Survey, p. 438. 



