226 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



show the hornblende enclosing small feldspars and suggesting at once 

 a close relation to the groundmass structures of the j)orphyry above. 

 In the feldspar crystals, particularly the larger ones, distinct outlines, 

 sometmies marked by the inclusion of small crystals of aegirite, of 

 an inner zone of growth may be seen. This boundary marks the 

 slight halt in the growth of the earlier formed crystals which is so 

 clearly shown in the granite-porphyry as will be noted later. 



Chemical Characters. — For chemical analysis a number of good 

 sized fragments were broken from carefully selected samples of freshly 

 quarried rock from the three localities listed below, one from well 

 toward the eastern end of the Quarry section, one from j of a mile 

 west of the first and the third J of a mile still further west, in the west 

 Quincy district. A sample of the porphyritic phase of the granite 

 from Rattlesnake Hill very near the granite-porphyry cover was also 

 analyzed. Great care was exercised in avoiding xenoliths or parts 

 that shoAved any discernible variation in grain. The percentages 

 given are the average of closely agreeing duplicates, except that the 

 values for ferrous-iron and alkalies are the average of three determi- 

 nations each. The methods of analysis advocated by Hillel)rand 

 were strictly adhered to. The results are given on page 227. 



For the convenience of those who have adopted the so-called " Quan- 

 titative Classification of Igneous rocks "^^ the "norm" has been calcu- 

 lated from the average of 1-2-3 given under 4. 



Sal IP ^ 7 



= 16 > 1. 



Class I 



Fern 



> 93 . 70 Salic Minerals, 



p = .52 < 5 > 7 order 4; quardofelic 



K2O + NasO .7 ^ 1 Tj 11 r 

 Qjg > T = Kang 1; reralkalic. 



5 . 84 Femic Minerals 



Na26 ^ . 75 < I > I = Subrang 3 ; Sodipotas- 



sic ; Liparose. 



The rock may, therefore, l)e termed a gruno-liparose or more exactly 

 an alkali-hornblende-aegirite grano-liparose. The calculation of the 

 mineral composition of the granite can only be made approximately, 

 since an accurate estimate of the amount of each mineral present 



24 Quantitative Classification of Igneous Rocks, by Cross, Iddings, Pirsson, 

 ^^'ashington, Univ. of Chicago Press, Chicago, 111., 1903. 



