LINDOEEN.] COMPOSITION OP THE COUNTRY ROCK. 641 



little orthoclase lies between the plagioclase grains. The biotite 

 occurs in small foils of brownish yellow color. Magnetite occurs 

 sparingly. Titanite is much more abundant, occurring in large crys- 

 tals or anhedrons, sometimes wedge-shaped. It includes small feld- 

 spar grains, but its crystals also project into larger feldspar grains. 

 The structure of the rock is eugranitic. 



An approximate calculation of the analysis of the fresh rock (I) 

 may be made in the following manner : On the basis of a preliminary 

 calculation and estimate there is about 15 per cent of biotite present. 

 For this 1.20 per cent potassa was subtracted. The baryta is calcu- 

 lated as hyalophane, which necessitates a deduction of 0.12 per cent 

 more of potassa. The remainder is calculated as orthoclase. The 

 lime needed for calcite, titanite, and apatite is subtracted from the 

 total lime. The amount of magnetite is estimated. Finally biotite 

 and quartz remain. From the amounts of the bases in this remainder 

 it is estimated that there is 25 per cent free quartz present. 



SiO 2 - 6.51 



A1,O 3 - 1.85 



K,0 - 1.70 



KAlSi 3 O 3 10.06 



SiOi - - 20.78 



. AI 2 O 3 --- 5.90 



-- ---- -- 3.57 



NaAlSi 3 O 3 --.. 30.25 



SiO* --- 6.00 



A1 2 O 3 --- 5.09 



CaO.. 2.79 



CaAl 2 Si. 2 O 8 ..... .. ...... ______ ..... ________ .......... 13.88 



SiO 2 ... ......................... . .......... _________ .59 



A1 2 O 3 ...... . ..... -. ..... ____________________________ .25 



BaO ...... ....... -. ..... ___________ ....... - ......... 19 



K 2 ................... -- .......... --- -- -12 



Ba Al,Si 2 O 8 2KAlSi 2 O 8 __.- ....... . ..... .. ............. 1.15 



PA - .................. --------- ................ 19 



-.-- ...................... - ........ --- ......... 25 



Apatite ....... . ............................... ------- .44 



Ti0 2 ..... . .......... - .......... - ............... --- -66 



Si0 8 _____ .................. _______ ............ - ....... 50 



CaO ........ . ........ -.-- ............. _____ .49 



Titanite ...................................... - ..... 1-65 



FeO ........ ....... . ................. - ............ -20 



Fe 3 O 3 ______________________ .......... 



Magnetite ............ . ........... - ............... -61 



CaO ............................ ..................... 32 



C0 2 ..... i .............. - ........................... -.25 



Calcite . _____ ..... . ........................... ---- 



Quartz. ..... . ....................................... 25.00 



18 GEOL, PT 3 - 41 



