98 QinCKSILVEli DEPOSITS OF THE PAGIFIO SLOPE. 



Ilmenito in part converted to leucoxene is abundant in this as in most 

 of the pseudodiabases and pseudodiorites. A complete analysis of this 

 rock gave the following result : 



Loss at 100^, IPO 0.27r, 



Loss above 100°, H-0 1-1"9 



Silica, Sio- -la-oso 



Pliosplioric acid, r-O" 0-232 



Titanic acid, TiO= 1-"21 



Alumiua, Al-0^ 14.66:3 



Ferric 0-s.ide, Fe-O^ l-f»4G 



Ferrous oxide, FeO f- "32 



Maugauous oxide, MiiO 0. 151 



Lime. CaO !"■ 091 



Maguesia, MgO li- ®W 



Soda, Na-0 ^- -''9' 



Potassa, K=0 P- 1^9 



Total 100.482 



The atomic ratio deduced from this analysis is H" : R" : fi;''' : Si=: 

 0.162 : l.llfi : 935 : 3.272. 



No. 11, Knoxville, appears macroscopically a green, much-altered 

 sandstone, intersected by numerous minute veins of white mineral. Under 

 the microscope it is found to be a holocrystalline pseudodiabase consider- 

 ably decomposed. The feldspars are in part granular, but chiefly lath- 

 shaped crystals from O.l"""" to 0.4"'" in length. They are mostly clouded by 

 very small interpositions. The greater part show polysynthetic structure, 

 and the highest angles of extinction found were from 16° to 18° on each 

 side of the twinning plane. The fine grain of tlie rock and the presence 

 of much epigenetic chlorite make separation difficult. It was found, how- 

 ever, that the last precipitate fell at a density of 2.63, and there is there- 

 fore little orthoclase, if any, in the rock. The feldspar must be chiefly, if 

 not Avholly, oligoclase. 



The veins in this slide are filled for the most part with beautiful 

 prismatic crystals of plagioclase mixed with calcite. The augite occurs 

 as imperfect prismatic crystals and grains, either included in the feldspars 

 or between the crystals of the latter. Its color is very faint ; it is not 

 dicliroitic and o-ivcs cliaracteristic extinctions. Tlie large amount of chlo- 



