THE DECCAN TRAPS 769 



the composition Ab 1 An 2 , is constant and abundant in all; but neither the 

 highly sodic plagioclases, oligoclase or andesine, nor orthoclase were de- 

 tected. iVugite is also very abundant in the more holocrystalline types, 

 but becomes less so as the glass content increases, and seems to be quite 

 absent in one or two highly glassy specimens. It is gray or, rather more 

 often, slightly brownish, but non-pleochroic. Dr. H. E. Merwin kindly 

 examined the augite of the specimens from Chindwara, Seoni, and Nee- 

 much. He found that the optic axial angle 2 V is very small, up to about 

 30 degrees in the plane of symmetry, and obtained the refractive indices 

 a = 1.700 — 1.710, and y =■ 1.725 — 1.735. These values correspond to 

 those of an enstatite-augite, and it is of interest to note that Holmes 

 found enstatite-augite to be the common pyroxene in the Arctic basalts, 

 as will be noted later. Labradorite and augite make up about 90 per cent 

 of most of the holocrystalline specimens. Very small amounts of olivine 

 occur in one or two specimens as small, well formed phenocrysts. Irreg- 

 ular grains of magnetite are rather common, and the presence of some 

 leucoxene indicates that this is titaniferous. Very thin plates of ilmenite 

 also occur in a few specimens. Apatite is to be seen here and there, but 

 is not abundant. 



The specimens may be referred to four fairly well distinguished tex- 

 tural types, to each of which a few words may be given. 



(a) Coarse, holocrystalline, ophitic. — Specimens belonging to this type 

 come from Kolhapur* (30/366 ) 6 and Nasik,* in the Bombay Presidency; 

 Balaghat (982) and Jamirapat (30/364), in the Central Provinces; and 

 Giridih (3017), in Bengal. 



Megascopically, this type is fairly coarse grained and doleritic, black 

 in color, though the specimen from Kolhapur is decidedly brownish. 

 There are no phenocrysts and none of the specimens is vesicular. In 

 thin section they show a typically ophitic texture, the well-twinned labra- 

 dorite being in sharp tables up to 2 millimeters in length, with anhedral 

 augite intersertal between them . The augite is generally slightly brown- 

 ish, though the Balaghat specimen contains considerable purplish augite 

 along with some that is colorless; but this specimen appears to be not 

 quite fresh. The augite contains some magnetite grains as inclusions. 

 but no feldspar or glass. The specimen from Nasik is the only one that 

 contains olivine in fairly well formed phenocrystic individuals. Magnet- 

 ite is rather abundant, generally in irregular grains, but in the Giridih 

 specimen much of it is in thin plates. It is probable that all the magnet- 

 ite is titaniferous. A few small apatite needles are to be seen, but there 



1 



6 The numbers in parentheses are those of the India Geological Survey. An asterisk 

 denotes that the specimen has been analyzed. 



