GEOLOGY OF THE HAYSTACK STOCK 221 



or decrease with the silica. The variations of the oxides in the 

 Haystack series, with respect to silica and to each other, are much 

 less regular than is the series at Magnet Cove. This is well illustrated 

 by the crossing descending lines in the diagram. 



Probable average composition 0} stock. — The average composition 

 of the six analyzed varieties of the Haystack stock is as follows : 



AVERAGE CHEMICAL COMPOSITION OF THE SIX ANALYZED VARIETIES 



SiO. 57-32 H,0+ 0.83 



AI2O3 : 16 . II TiOs o .83 



Fe^Oa 3. IS CO2 0.07 



FeO 405 P2O5 0.33 



MgO 4.16 MnO o.ii 



CaO 6.61 B aO o . 09 



NajO 3-46 SrO o . 03 



K2O 2.40 



H2O — o . 25 Total 99 . 80 



NORM OF THE AVERAGE OF THE SIX ANALYZED VARIETIES 



58 Magnetite 4.41 



46 Ilmenite i .52 



34 Water i .08 



13 Fluorine o . 67 



51 



Quartz 8 



Orthoclase 14 



Albite 29 



Anorthite 21 



Diopside 8 



Hypersthene 10 ■ 37 Total 100 .07 



This is probably very close to the average composition of the stock, 

 and is perhaps as good an estimate as could be made with the data 

 at hand. Its composition closely resembles that of a large number 

 of orthoclase-gabbro-diorites, andesites, and related rocks from 

 Crandall Basin and Sepulcher Mountains, described by Mr. Iddings,^ 

 a number of monzonites and andesites from Colorado, described by 

 Dr. Whitman Cross,^ and diorites from Mt. Ascutney, Vt., described 

 by Mr. R. A. Daly.^ Of the Haystack rocks the average is nearest 

 C, which is a contact facies of the stock. 



Asymmetry 0} the stock. — The map (Fig. i) shows that the Hay- 

 stack stock is asymmetrical. The stock is also asymmetrical with 

 respect to its composition. Fig. 3 is a sketch map which shows the 



1 Mon. XXXII, U. S. Geological Survey, Part II. 



2 Bulletins I and 168, U. S. Geological Survey. 



3 Bulletin 14S, U. S. Geological Survey, p. 69. 



