DECCAN TRAP IRON-CLAY. 219 



eolation of watei', must tend to diminish daily whatever difference origin- 

 ally existed between the products of the two several kinds of rock affected. 



As above mentioned, the passage downward of the base of the iron- 

 clay into gneiss is to be seen very clearly in various sections in the 

 scarped edges of the iron-clay plateau, also in the beds of some nullahs, 

 e. g., the Gauli nullah and the stream flowing westward from Talewari 

 (Tullwaree) . In the latter the descent from the pure iron-clay into de- 

 composing gneiss is very clear, the quartzose laminae of the latter re- 

 maining in situ after the softer parts have all been replaced by the clayey 

 masSj and standing up in the latter for a distance of many inches. The 

 undecomposed gneiss is not seen in any of these sections. 



In the small stream rising south-westward of Meindil (Meindool) 

 south of Talewari, the passage of a micaceous schistose gneiss upwards 

 into iron-clay is very clear, as the stages of decomposition of the older 

 rock are well exposed in the bank of the stream. 



The iron-clay is not unfrequently a breccia in structure, owing to the 

 presence of numerous small angular fragments of white vein quartz, which 

 are very frequently seen in similar iron-clays far away from the gneiss 

 rocks, and about the wholly trappean origin of which there can be no 

 doubt. 



The source of these quartz fragments has yet to be traced ; they are 

 Origin o£ enclosed '^^^ derived from the trap rocks themselves, as the 

 quartz fragments. latter do not contain quartz in their composition in 



this form, nor are they derived from the breaking up of amygdaloids, nor 

 is it easy to see how they could have been derived from a quartz formed 

 dm'ing the decomposition of the trap, which would show a nodular, if 

 not positively concretionary, structure. No trace of such structure could 

 be seen on any of a very large number of the quartz fragments and 

 splinters in the breccias. 



The exceeding rarity of geodic quartz in these subaerial iron-clays 



Absence of geodic ^^ ^'^^ ^ difficulty of which I cannot offer any 



*^^ solution. Common as are the amygdaloid geodes 



( 219 ) 



