1836.] 



Neelgherries and Koondahs. 



255 



subject, a year ago, when my early observations on the Geology of the 

 Neelgherries appeared in the Bengal Journal. This rock results from 

 a modification of structure, and a change of texture in the heematitic 

 iron-ore ; which (as well as the magnetic species of the same metal) 

 in India forms enormous beds, whole hills, and ridges ; and therefore 

 must be considered as a vein or a bed of this metal, like the titanife- 

 rous iron ore, the magnetic species, the chromate, the one with man- 

 ganese, &c. which all are imbedded, or impacted substances, and not a 

 principal rock, so as to deserve the name of a distinct formation, dif- 

 ferent from the other members of the same family, because it is cellu- 

 lar ; we might as well call burnt clay pumice-stone because of its cellu- 

 larity. The change of structure of this rock consists, in becoming, 

 from compact, cellular, but hardly ever tubular, with a surface rough 

 and bristled with asperities ; in a few blocks some of the cavities are 

 lined with a yellowish substance ; it hardly ever contains quartz or sand ; 

 but often small pieces of compact felspar, in a decomposed state ; oc- 

 casionally it has a breccioide structure. 



Whatever might have been, or is, the cause of this change in the 

 appearance of this ore, it is connected with atmospheric vicissi- 

 tudes. To prove what I have been hitherto describing, regarding this 

 modified iron ore, that it is nothing else than a mere change in appear- 

 ance, and not a new rock, I have specimens in my possession, and have 

 deposited others in the Museum of the Madras Literary Society, which 

 shew in the small thickness of an inch, or little more, the ore chang- 

 ing from compact haematite into lateritic iron ore. 



This iron ore disintegrates, the pieces getting rounded, for reasons 

 not easily explained, and are either scattered about the soil, or re-agluti- 

 nated by a clayey paste forming a conglomerate ; which either adheres 

 to the lateritic rock or to the ore itself. If these rounded pebbles are of 

 moderate dimensions, and of different sizes, a conglomerate is the result 

 perfectly similar to the conglomerate laterite of the Carnatic ; but, 

 when the pebbles have an uniform size, and are not larger than a pea, 

 then it becomes the common pisiform iron ore, the pisiform clay-iron- 

 stone of authors. In this state, the rock has different degrees of compact- 

 ness from crumbly to compact ; in which last case it is employed for 

 architectural purposes. This detrital rock sometimes is seen at some 

 distance from the iron ore. 



The third species, w ? hich abounds all along the intervening land, from 

 the foot of the western ghauts to near the sea shore, resembles very 



. i\ much the modified heematitic iron ore (not the pisiform) being cavernous, 



> ) not tubular, abounding with quartz pieces and sand j having not only 

 : the cavities lined with powdery felspar, but, in the compact portion of 



y the rock, having small pieces of the same mineral in the compact state. 



is The late Dr. Christie tells us that it is remarkable, that this rock 



