STRATIGRAPHICAL FEATURES. 25 



able from the lavas, which must have been injected after the consoli- 

 dation of the granite. The granite must have been intruded after a 

 sufficient depth of lava had accumulated to allow of the crystallisation 

 of the material in a coarse grained form, but before the extrusion of the 

 lavas had ceased. The granites may, therefore, be considered as 

 strictly contemporaneous with the lavas, and it is not at all improba- 

 ble that they marl: the approximate sites of some of the vents or 

 fissures from which the latter were poured out. 



5. Basic dykes. 

 The volcanic period was succeeded by the intrusion into the 

 complex of lava and granite of a number of basic dykes, the 

 material of which is an altered olivine dolerite or diabase consisting 

 of plagioclase felspar, olivine and augite with a small amount of 

 biotite. The interval that elapsed before the intrusion of these dykes 

 cannot be ascertained, but it must have been sufficient to allow of the 

 development in the lavas and granites of joint planes, since the dykes 

 usually follow such planes. The majority of the dykes run north and 

 south, but another system crosses these almost at right angles. There 

 does not seem to be any difference in composition between the rocks 

 of each system. They appear to have been injected before the de- 

 position of the overlying Vindhyan sandstones, since they have not 

 been found traversing these, but as it happens, none of the dykes 

 were observed, even among the lavas, in that part of the country 

 where the remnants of the sandstones are now visible, and it is quite 

 possible that the dykes are of post-Vindhyan age, Mr. Blanford 

 mentions an outburst of " basalt " in connection with the Talchir 

 boulder beds of Pokaran, but he says that the relations of the rocks 

 are not clear. 1 



1 Roc. Geol. Surv. Ind., Vol, X, Pt i, p 13. 



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