436 Pirsson and Washington — Geology of Red Hill, N. H. 



I. Microscopical analysis of phyro-miaskose, Red Hill, N. H., 

 by L. V. Pirsson. 



II. Chemical analysis of grano-miaskose, Home Quarry, Red 

 Hill, by H. S. Washington. Includes S0 3 , 0*08. 



III. Chemical analysis of tracho-umptekose, Red Hill, by W. 

 F. Hillebrand, includes MnO, 0-03, BaO, 0-08. 



The composition thus calculated is very similar to the other 

 ones already given, especially to that of the grano-miaskose, as 

 may be seen in the table. The water is all from the biotite \ 

 ZrO„ is probably too high. 



Texture. — The texture of the groundmass is a purely 

 trachytic one, caused by the slender lath-like feldspars. 

 These are scattered, pointing in all directions, but groups of 

 albites tend to be subparallel or divergent in places ; no fluidal 

 texture was seen. 



Classification.- — In the quantitative system the place of this 

 rock is shown by its norm, calculated from the microscopic 

 analysis, to be as follows : 



Norm 

 Or _. 4281 



Ab.. 29-34 Sal 91-21 



An.. 0-56 Fen7 = ^74" = H +, I, Persalane 



Ne.. 14-20 L 1850 



So.. 4-30 Sal = 91-21 -y- = ? ^ = 0'25, 6, Russare 



5! "" iVr, K„0' + NaO' 201 , r . , 



Ol .. 0-10 2 ,Z ' = -— = 22, 1, Miaskase 



Mt.. 4-87 t-™ 



II .. . -80 Fern = 7*74 K 2 ° _ 21. - n -«9 w i Miaskose " 



Zr .. -70 Na 2 0' ~124 ' ( Beemerose 



HO. 45 



Total 100-10 



Comparing the norm with the mode, it may be noted that 

 the biotite and aegirite have disappeared, while orthoclase and 

 magnetite have much increased. The potash of the modal 

 nephelite has increased the normative orthoclase and has been 

 replaced by the soda of the aegirite, the amount thus remain- 

 ing the same. The lepidomelane has split up into orthoclase 

 and magnetite, the iron of the aegirite aiding. The biotite and 

 aegirite-augite of the mode form about 16 per cent and are 

 not present in the norm ; the mode is therefore an abnormative 

 one. The texture is porphyritic and microscopically trachytic 

 and the rock may therefore be termed biotitic-trachiphyro- 

 miaskose. In the older systems it would be a nephelite- 

 syenite-porphyry. 



