1S38.] 



On the Latentic Formation. 



339 



appearance may be accounted for. The first may be shewn in the fol- 

 lowing manner. A rock containing a large proportion of quartz decom- 

 poses ; the softer parts crumble into earth, or form a red ochreous ce- 

 ment, which binds together the quartz in a state of pebble, and ferru- 

 ginous from the infiltration of oxyde of iron — this, after a time, when 

 broken into, has a somewhat cellular and tubular structure, from the 

 irregular junction of the pebbles leaving interstices or cavities between 

 them — this cavernous structure being at the sam.e time increased by the 

 falling out of the earthy and softer parts. A hiterite of this nature 

 is found above the ghauts, between Manantoddy and the Neilgherries, 

 in the Wynaad jungle, near Sultan's Batterv. It is found protruding from 

 the ground on the road, and is externally of a dark black colour — surface 

 irre9:u''ar, and full of cavities, with pieces of quartz crvstal attached to it ; 

 internalb/, it is of a blackish brown colour, with irregular cavities, and 

 also containing small pieces of quartz. It appears to be a quartz rock, 

 which has undergone oxydation and decomposition. When the quartz 

 did not form into a laterite, it decomposed into a species of ferruginous 

 sandstone, like what iron is obtained from in some parts of Mysore. 

 "With the exception of talc slate I saw nothing but the quartz, laterite 

 and quartzose sandstone in the locality now referred to— the two last 

 being the result of decomposition, the sandstone arising from the decom- 

 position of granular quartz of a loaf-sugar aspect, but ferruijinous colour; 

 and the laterite arising from the oxydation and decomposition of a large 

 crystalized smoky coloured quartz. It must be borne in mind, that 

 when I speak of a quartz rock I mean a rock containing chiefly quartz, 

 but not entirely excluding felspar. 



This is the place to describe the laterite of the Neilgherries ; and its 

 varied appearance and connection with what in the geology of those hills 

 has been cal'ed hfematitic iron ore, confirms me in my opinion that not 

 only is laterite a rock of oxydation and decomposition, but so also is the 

 hfEmatitic iron ore, or rather that which has very improperly been 

 iiamed so. It may be as well first to observe, that tli*^ principal rock on 

 the Neilgherries is a hornblende rock, or a sienitic granite — one passing 

 constantly into the other ; frequently exhibited even in hand specimens. 

 The quartz which has a tendency to run in veins, is of a very peculiar 

 opaline colour, and in rather large crvstals. In all the sections, immense 

 veins of this quartz are in a decomposing state, and it is in these that the 

 iron ores, so prevalent on the hills, are found. In very many localities, the 

 garnet is a most abund mt mineral, som.e specimens shewing more of it 

 than of either hornblende or quartz ; so that the principal rock might be 

 called a garneti-: sienite or a gametic hornblende rock. Besides these 



