ALLUVIAL DEPOSITS. ». 



of the strata is locally greater than here, I have not observed a single case of 

 quartz-veining ; and in other basins of these formations the thing is almost un- 

 known. There is, however, one marked feature of these veins that has long been 

 familiar to us in many parts of India in metamorphic and transition rocks— a 

 peculiar pseudomorphic structure; thin shining plates of pearly white quartz 

 either in parallel arrangement or confusedly entangled, with empty interstices. I 

 do not recollect noticing this form in vein-stones in other countries, but in India it 

 seems to be nearly universal. The fine lines on these shining plates have suggest- 

 ed that they may be after micaceous iron. Stains of iron are common, but there 

 are no signs of any other metal in these veins. There is often associated brec- 

 ciated quartz." 



As far as my observations go they often have no connection with 



faulting, in which cases the strata are little, if 



Associated with faults. * " 



at all, disturbed in their neighbourhood ; but as 



on the Lodadeo-Rawandeo ridge, at the Pothia and Saleye faults 

 they are certainly associated with the faults. There is no reason 

 however, to suppose that they owe their origin to the faulting except 

 in so far as that would form numerous crevices and cracks favour- 

 able to the deposition of the silica. Their formation was long sub- 

 sequent to the faulting and the resemblance of the plates of 

 which they are so often composed, to the form assumed by mica- 

 ceous iron, points to the conclusion that at one time the room now 

 filled by the silica was formerly occupied by other minerals which 

 were only subsequently slowly, but entirely, replaced by means of 

 infiltration. 



§ 21.— 'Alluvial Deposits, 



In the river valleys there are alluvial deposits being formed along 

 the banks of the rivers, consisting of the materials washed down from 

 higher ground. One important constituent of this deposit is formed 

 by trap in the form of rolled boulders derived from the surrounding 

 trap hills, and which at times occur closely packed together with the 

 sand and clay which alone are seen in other parts. These deposits, 

 where they occur, hide a great portion of the older rocks. 



( 53 ) 



