84 VREDENBURG : RECENT ARTESIAN EXPERIMENTS IN INDIA. 



(S) The Deccan Trap. 



A system of rocks whose capabilities as water-bearing strata caH 



Need of more accurate for further research is the volcanic series known 



information. as the » Deccan Trap.*' The immense area 



occupied by that formation has almost entirely escaped geological 

 investigation. The series consists largely of basalt, a rock of highly 

 impermeable texture, but it is not known to what extent the exist- 

 ence of fissures and caverns may not affect its capacity in that 

 respect. In some parts of the Bombay Presidency wells have been 

 known to derive an abundant supply of water from fissures in the 

 basalt. 



Moreover, the formation does not consist entirely of basalt : in 

 some parts the sheets of basaltic lava are in- 



Composition, 



terbedded with great masses of tuff of more 

 or less open texture. During intervals between the volcanic erup- 

 tions fresh water lakes were formed, in which sediments, the so 

 called" intertrappeans," were deposited. Some of them are very 

 compact limestones, but others are sands of loose texture. All 

 these fragmentary rocks, tuffs, and intertrappeans might occur so 

 placed as to form artesian reservoirs. But in our ignorance of the 

 geological details of the formation, the existence of such reservoirs 

 can only be indicated as a bare possibility without any reference to 

 particular localities. 



In the western portion of their outcrop, near Bombay or in 

 Gujarat and Kathiawar, these rocks have under- 



Structure. 



gone a certain amount of disturbance. But in 

 all other parts of the area occupied by the Deccan trap, the rocks 

 are quite undisturbed and almost horizontal. Perfect horizontality 

 of stratification would be incompatible with the existence of an 

 artesian reservoir, unless accompanied (as it is sometimes) by 

 irregularities of water-bearing capacity at various places. But it 

 stands to reason that the horizontality of the strata that compose the 

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