1838.] 



On the Latcriljc Foiiiiation, 



341 



pisiform iron ore, both of wbicli are extremely light, containing, I sus- 

 pect, little or no iron, and do not, in my luiuible opiuion, deserve at all 

 the name of iron ores. I cannot help considering both of them as differ- 

 ent stages of alteration and decomposition of the rock in s'Uii, containing 

 much quartz, and that large grained opaline quartz which has been de- 

 scribed. I have preserved what I consider the different stages, and 

 I think that when much felspar or hornblende has entered into 

 the original rock, the specimens of this so named hcematitic iron ore are 

 decidedly lateritic. Dr. Benza's mind does not seem to have been made 

 up on the subject of what he proposes to call the lateritic iron ore, and 

 which he wishes to distinguish from true laterite. His observation, that 

 many of the hard blocks of this conglomerate, alluding to his hasmatitic 

 iron ore, resemble very much, if they are not identical v>dth, tlie laterite 

 of the low lands of India, confirms me in considering his heematitic iron 

 ore, and lateritic iron ore, as only different stages of decomposition and al- 

 teration, both being the result of oxydation and decomposition. I pos- 

 sess specimens of real hematite, picked up on the hills, with most mark- 

 ed characters, and not for an instant to be mistaken for that which is so 

 common, just described. "Why sliould not true laterite exist there, as at 

 Coorg and on the coast, v/here there are the same class of round liiho- 

 marge hills, the same ferruginous character of the rock, and in a certain 

 degree the same character of climate, as far at least as regards rain^ 

 which, falling in such abundance, must predispose both to oxydatio^ 

 and decomposition. 



The geology of the Neilgherries is extremely simple — a horn- 

 blende rock or sienitic granite, with numerous quartz veins con- 

 taining various iron ores, has decomposed to a very great extent. The 

 hornblende and felspar have formed the lithomargic earth so abundant 

 there ; these two substances being so easily decomposable, leaving occa- 

 sionally on the surface masses of quartz rock, which, although resisting 

 total decomposition, have undergone alterations, and been converted 

 either into Benza's ha-matitic or pisiform iron ore; this altered quartz 

 rock containing within it sometimes either magnetic or titaniferous iron 

 ore, besides the true hajmatite, which must not be confounded with the 

 rock in which it is imbedded. If any thing stronger is required, and the 

 above not considered satisfactory, I would refer to an analysis by my very 

 talented friend, Mr. Gilchrist ofHoonsoor. He sent specimens of a rock 

 very common in his neighbourhood to Br. Benza who informed him that 

 they were the same as described in his geology of the Neilgherries 

 under the name of haemati tic iron ore. Nov/ Mr. Gilchrhst, perceiving 

 that they were so extremely light as not, in his opinion, to deserve thf' 

 name of iron ores, put them to the test of analysis, and found tl-.at in- 



