1897.] Petrography. 607 
SiO TiO POs; AlO; FeO, Feo CaO MgO K,0 Na: H,O l 
54.15 tr 18.25 3.62 2.09 4.89 2.56 6.56 4.43 3.69 = 100.65 Density = 2.632 
The basalts include feldspathic, nephelinic and magma basalts, 
analysis of the first two of which are here given : 
SiO, TiO, POs AlO; FeO; FeO CaO MgO KO NaO H,O CO: Total 
42.75 2.13 tr. 17.24 810 588 1114 617 248 4.21 = 101.16 
39.33 1.01 .93 15.26 636 5.99 1452 9.78 1.53 3.47 2.54 0.12 — 100.84 
The tephrites are phonolitic and basaltic hauyne-tephrites, sodalite- 
tephrites, nepheline-tephrites. and leucite-tephrites. The phonolite 
contains great quantities of anorthoclase in large crystals. Some 
phases of the rock are noticeable for their phenocrysts of sodalite and 
others for their phenocrysts of nepheline. The other rocks possess no 
special features. 
The Law Governing the Production of Zonal Crystals. — 
The law governing the occurrence of zonally developed crystals is as 
follows, according to Becke*: In the zonally developed isomorphous 
mixed crystals of igneous rocks the more difficultly fusible components 
constitute the nuclei, and the more easily fusible ones the peripheral 
zones of the crystals. 
Petrographical Notes.—Diller’ has discovered a boulder of horn- 
blende-basalt in Kosk Creek at the great bend of Pitt River in Shasta 
Co., Cal. It is interesting not so much because of its features, but be- 
cause of the rarity of the type in the district. An analysis yielded : 
SiO, TiO, AlO, FeO; FeO MnO CaO MgO KO NaO H,O P,O; Total 
44.77 53 17.82 505 6.95 tr. 10.36' 8.2292 2.18 264 :72 — 100.11 
The Seychelles Islands in the Indian Ocean are described by Bauer’? 
as being composed principally of hornblende, granite and of syenite cut 
by dykes and covered in places by sheets of granite-porphyry, felsite- 
porphyry; syenite-porphyry, hornblende-vogesite, diorite, quartz-diorite, 
diabase, melaphyre and dolerite. The sedimentary rocks on the island 
are in very small quantity. They consist mainly of andalusite-horn- 
fels and other contact rocks. 
ê Min. u. Petrog. Mitth., Vol. XVII, 1897, p. 97. 
° Amer. Geologist, Vol. XIX, 1897, p. 253. 
1 Sitzb. Ges. z Beford gesammnt. Naturw. zu Marburg, Feb., 1897. 
