( 412 ) 



I Yentnite, Yentna River, Alaska ; anal. H. N. Stokes, cf. J. Ë. 



Spurr, Am. Journ. Sci. X, 310, 1900 (Tonalose; included 

 in the sum : S = 0.02, and traces of 01, SrO, Li 2 0). 



II Biotiteamphiboleandesite, right bank of Tëbaoeng-river, opposite N a . 



Oeroei, Central-Borneo, anal. M. Dittrich. (Tonalose). 



III Andesite. Pnnta della Civitate, Capraja-isl., Italy, anal. A. Röhrig, 



cf. H. Emmons, Quart. Journ. Geol. Soe. XLIX. 142, 

 1893 (01 = 0.07 ; Tonalose). 



IV Hypersteneaugiteandesite, Palisades, Crater Lake, Oregon, anal. 



H. N. Stokes, cf. H. B. Patton, Bull. U. S. Geol. Surv. 



168, 22:!. 1900 (SrO = 0.07; Tonalose). 



V Hornblendeporphyrite, Nevada City, Calif., anal. H. N. Stokes, cf. 



W. Lindgren XVII Ann. Rep. U. S. Geol. Surv. II, 59 ; 

 1896 (S0, = 0.10; Tonalose). 



VI Pyroxenemicadiorite, Electric Peak. Yellowstone Nat. Park. ; anal. 



W. H. Melville, cf. J. P. Iddings, XII Ann. Rep. U. S. 

 Geol. Surv. I. 627, 1891 (NiO = 0.09, Tonalose). 



IV. ApKtic Microgranite (normal. Graniphyrilassenose). 



The rough, pure white, powdery, very tine-grained rock often 

 contains holes, in which appear mica-rosettes and serpentinous products, 

 which also in microscopic aggregates lie scattered through the whole 

 rock and by this betray a certain porosity. 



The proper rock-components are mostly rather fresh and in keeping 

 with this the appearance of the secondary products — among which 

 the muscovite takes a foremost place - - seems with great probability 

 to have to be attributed to pneumatoly tic processes, not to atmospheric 

 weathering. The structure is holocrystalline porphyric, but as such 

 it is only to be recognized microscopically. The very few phenocrysts 

 (average diam. 0.3 mm.) consist of a Ibite ; they show a little developed 

 idiomorphy, are seldom twinned after the albite-law, but often occur 

 irregularly grown together into groups of 2 — 3 individuals. A begin- 

 ning of decomposition shows itself in the appearance of opaque 

 globulites, principally arranged parallel to the cleavage-directions. 

 Quartz and orthoclase-phenocrysts are entirely wanting. The holo- 

 crystalline groundmass consists of lathshaped, seldom tabular, strongly 

 undulous, and always after the albite-law twinned, irregularly diver- 

 ging, now and then parallelly arranged acid plagioclases, cemented 

 by grains of quartz with sometimes tolerably pronounced idiomorphy, 

 then, however, always peripherically cut asunder fringelike by feld- 

 spar, mostly, however, without indication of crystal lographic boun- 



