1893.] Mineralogy and Petrography. 381 
massive rocks associated with the contact products. Diabases occur as 
sheets in the unaltered paleozoic beds, and serpentines derived from 
gabbros and from dunites are met with cutting these at various locali- 
ties. In addition to paleozoic there are also tertiary rocks on the 
island, and these are cut by their own systems of dykes and bosses, and 
are interbedded with characteristic sheets of lava, and layers of tufas. 
The tertiary voleanic rocks are pyroxene and hornblende andesites, 
propylites and rhyolites. The pyroxene andesites contain both ortho- 
rhombic and monoclinic pyroxenes and occasionally some olivine. 
They have also a glassy base which sometimes becomes so abundant as 
to 'resemble pumice. The hornblende andesite is strongly porphy- 
ritic with large phenocrysts of hornblende. The rhyolites are both 
compact and glassy, in which latter case they are vesicular. 
Two Peculiar Rocks from Siberia.—Two very remarkable 
rocks are described by von Chrustschoff* from Taimyr-Land, Siberia. 
One is an ophitic aggregate of anorthoclase and nosean, containing as 
accessories sanidine, plagioclase, amphibole, biotite, melanite, magne- 
tite, sphene, zircon and glass. The anorthoclase is in long, narrow 
crystals of the following composition : 
SiO, AlO, FeO, CaO MgO K,O NaO Total 
64.59 19.84 2.24 1.26 .63 3.3 7.88=99.97 
Corresponding to Or, Ab, An, The feldspar is usually idiomorphic 
with respect to the nosean, whose period of formation was between 
that of the biotite and that of the hornblende. The nosean is in very 
large quantity. Its density is 2.266 and composition : 
SiO, AlO, FeO, NaO K,O CaO H,O Cl SO, Total 
37.83 2659 .38 2240 1.63 .54 .87 1.66 8.68 — 99.98 
The zircon is of the trachytic type, and is the only accessory of any 
importance. The author calls the rock taimyrite. The second rock 
is composed of anorthoclase, sanidine, biotite, and amphibole as essen- 
tial components, and the other minerals mentioned above in connec- 
tion with taimyrite as accessories, except that sodalite here replaces 
nosean. The zircon is of the granitic type, and the rock possesses the 
granitic texture. 
5Bull. d. Acad. Imp.des Sciences St. Petersb. Mél. Geol. et Paleont., i, p. 153. 
