GEOGRAPHICAL DISTRIBUTION OF 



sanidine is only to be recognised by its crystalline form and optical 

 properties. Bastite is a product of the decomposition of enstatite. 

 Augite, like the plagioclase, contains inclusions of glass, but they 

 rarely show devitrification as in the felspar ; they are similarly asso- 

 ciated with steam pores, microliths, and occasional fluid inclusions. 

 Olivine and plates of mica are very rarely detected in the ground 

 mass. 



Quartz Augite Andesite. Zirkel divides augite andesites into 

 two groups according to the presence or absence of quartz. Most of 

 the andesite from the American Andes belongs to the quartz-bear- 

 ing variety, and contains from 57 to 67 per cent, of silica. It is 

 recorded, among other localities, as from Chimborazo, at a height of 

 17,916 feet, Gua^apichincha, Cotopaxi, Antisana, Riobamba, Tun- 

 guragua. At Palissade Canon in the Cortez range, in the region of 

 the Fortieth Parallel Survey, an exceptional rock of this kind occurs 

 with 62 per cent, of silica, which has a granular crystalline texture, 

 is free from glass, abounds in well- crystallised quartz, has no horn- 

 blende or olivine, and but little sanidine, and consists chiefly of 

 plagioclase, with some augite and brown mica. 



Distribution of Augite Andesite in Europe. The variety of 

 augite andesite which is free from quartz is found chiefly in lava 

 streams; it is seen in Iceland, at Hals, in the Hecla lava of 1845, 

 though the ashes of that eruption differ in chemical composition. It 

 occurs at Portillo in Teneritfe, at Serra Varalau, in the Yal del Bove. 

 It forms much of the volcanic summit of Radicofani in Tuscany, where 

 it contains olivine. The augite andesite of Reykjavik is of a greyish 

 or reddish colour, and consists of oligoclase, augite, and olivine, with a 

 felspar in loosely-connected thin plates. The rock which caps the 

 Lowenburg in the Siebengebirge appears to contain nepheline, and is 

 grouped by Zirkel as an augite andesite. The Transylvanian augite 

 andesites have a crystalline ground mass at Nagy Banya, but generally 

 the ground mass varies from a macrocrystalline to a microlithic state, 

 with the remains of a more or less glassy base ; and many varieties of 

 texture occur in these rocks at Tokaj, Schemnitz, and other localities 

 in Hungary. A black variety of the rock with a resinous lustre 

 occurs at Bagonya in Hungary. In the Auvergne, augite andesites 

 composed the lava-flows which ran down from the Petit Puy de Dome, 

 Parion, and from the Puy de la Nugere towards Volvic, where they 

 become crystalline. Augite andesites are well developed in Santorin 

 in the lavas of 1865. 



The South American augite andesites from Tunguragua, Cotopaxi, 

 and Antisana, though containing 63 to 67 per cent, of silica, contain 



quartz, but are rich in brown glass. 



North American Augite Andesites. To the south-west of Salt 

 ke, where an angular bend occurs, near the southern extremity of 

 the Cedar Mountains, is an outburst of andesite which occupies the 

 entire angle. In external appearance it is quite like basalt ; it occurs 

 in thin sheets, and often shows rude columnar joints. Where broken 

 it shows a large amount of pale grey glass, with crystals of plagioclase, 



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