794 H. S. WASHINGTON DECCAN SALTS AND PLATEAU BASALTS 



ophitic texture, being composed of tabular labradorite crystals, with 

 interstitial grains of a slightly brownish augite, some thin plates of 

 ilmenite (?), very few equant magnetite grains, and considerable brown- 

 ish interstitial glass. There are a few automorphic, but somewhat cor- 

 roded, crystals of olivine which is partially serpentinized. The thin 

 section much resembles those of some of the Deccan traps, especially that 

 of the olivine basalt of Nasik in Bombay. 



Table XI 



Analysis of Patagonian Basalt 



1 2 



Si0 2 48.36 50.74 



A1 2 3 12.01 12.60 



Fe 2 3 4.56 4.78 



FeO 6.91 7.25 



MgO 8.58 9.00 



CaO 8.48 8.90 



Na 2 2.47 2.59 



K 2 0.69 0.72 



H 2 0+ 2.76 



H 2 0— 1.46 



Ti0 2 2.60 2.73 



P 2 5 0.35 0.37 



MnO 0.30 0.31 



99.53 99.99 



A chemical analysis gave the results shown in Table XI, there being 

 given also in number 2 the figures for the major constituents reduced to 

 100 per cent after omission of water, as, the content in water is inordi- 

 nately high. It will be seen that the analysis resembles in general those 

 of other plateau basalts, except that the total iron oxides are somewhat 

 lower (even when the water content is eliminated), with ferrous oxide 

 not so highly dominant over ferric as in most of them and with magnesia 

 decidedly higher. The percentage of manganese is rather high, but those 

 for titanium and phosphorus oxides are about normal. It will be noted 

 that here, as was the case with the olivine basalt of Nasik, there is a very 

 decided excess of silica shown in the norm, as given below. This crys- 

 tallization of olivine in a magma that has excess silica, like that of the 

 Nasik basalt mentioned above, is in harmony with Bowen's 39 experi- 

 mental observations of the early crystallization of olivine and its later 

 resorption and the subsequent crystallization of enstatite. 



39 Bowen and Andersen: Amer. Jour. Sci., vol. 37, 1914, p. 49G ; N. L. F.owen : Amer. 

 Jour. Sci., vol. 38, 1914, p. 235. 



