346 J. J. Harris Teall—On Hypersthene Andesite. 
Some little difficulty was at first experienced in stopping the 
action of the acid at the right moment, but at last this was overcome 
and the mineral obtained in a really surprising state of purity and 
freshness. The felspar and pyroxene were then examined under 
the microscope and carefully picked over. 
Ls TT, 
8i0, Soman 55°06 Seta si 52°08 
AO eee ae eee 21°37 i eae 30°00 
BeOs SMa oh trace ee sce trace 
CaO bites ae 8°92 pais? dae 13°51 
MgO oie ecal] MRO b esti agers ee 65 
Nes Oba tee ay aes 4500 Wag Mae 3-24 
K,0 wus oh dees 1°30 ar ditgene “41 
97°64 99°84 
I. Porphyritic felspar. Cheviot Rock. 
JHE. x op Steinerne Mann Rock. 
* J regret that want of material makes it impossible for me to repeat this analysis. 
The composition of labradorite, according to Roth (Allgemeine 
und Chemische Geologie, p. 15), lies between the following limits :— 
SIO oa ee: PN leas 
ATS Oceby Sale 2S 4 On Wi | Wh i are 
CRORE pes iies POLSON pox ee minal ero 
ING Oe yueeet tgrciac 5°73 Soo nese 2°82 
It thus appears that the felspars are both labradorite, but that they 
differ in composition in the same way as the rocks themselves differ. 
There appears, therefore, as we should expect, a definite connexion 
between the composition of the rock and the composition of the 
porphyritic crystals. 
In the following analyses of the pyroxenes the material was taken 
air-dry, and the loss on ignition was not determined. The iron 
was estimated as Fe,O;, and is reckoned as FeO. MnO was not 
determined. 
if El: 
SiO; Whtdalvah Bosse te Bilt sagmeroron 
Al Overegeten ta ALSO eee 4°76 
BOO Obie: elOab Oy pane cabelas 
CAO) Caer eee AVG Re ree Wl ome 
MOE At) BOG aoa Mie) Sila ils Hatters 
98°31 98°59 
I. Cheviot pyroxene. 
II. Steinerne Mann pyroxene. 
filtering is to place a little asbestos at the bottom of an ordinary glass filter, as the 
dense liquid passes very slowly through ordinary filter-paper. The clear solution 
thus obtained will support fluor spar. My own stock solution has a specific gravity of 
3161. The above instructions are taken from a paper by V. Goldschmidt in the 
Neues Jabrbuch, I. Beilage Band, p. 179. The maximum density obtained by Herr 
Goldschmidt in the winter was 3°196. Any lower specific gravity may of course be 
obtained by dilution, and the original density may be again reached by evaporation 
over the water bath. 
