212 Mineralogy of Southern India. 



and sometimes irregular, according to its hardness. In 

 hardness, it is intermediate between dried earth and that of 

 clay-stone. In colour — red, when ferruginous : whitish, 

 when magnesian : reddish brown, when hornblendic. Is some- 

 times tufFacious. Forms the matrix of the magnesia form- 

 ation of Salem, and then contains magnesia. Becomes 

 silicious, and graduates into clay-stone when in contact with 

 quartz rock. Is commonly intersected into rhomboidal 

 masses by joints like trap. Is sometimes cretaceous, which 

 is not extraordinary, as trap is also generally associated 

 with kunkar. 



Magnesite, 



or more properly, the magnesia formation of Salem, is a 

 far-famed locality : it does not form hills, as is asserted in 

 some European publications, though it is sometimes found 

 in hills. At Salem it occurs as an extensive series of dykes, 

 injected veins, and reticulated veins, through other rocks. 

 Capt. Newbold has published an account of this formation, 

 and had I any hope of being able to visit the locality, and 

 give up a few weeks to its examination, I would not now have 

 noticed it. Unfortunately, while in the district, my official 

 duties prevented more than a few morning visits. I am un- 

 able to state the extent of the formation, but believe it can- 

 not be less than 25 square miles. It is white, hard, and com- 

 pact. Lens shews no granular structure. Hardness: variable, 

 from the toughness of a trap rock to nearly as soft as chalk. 

 Fracture : generally conchoidal, sometimes earthy. The hard- 

 est kinds do not effervesce with acids, but the softer do. 

 The wacke which forms its matrix, is slightly indurated 

 when in contact with the thickest dykes. It shews all the 

 signs of igneous action, injections, and squeezings, &c; and 

 is frequently very much contorted. Asbestiform minerals 

 abound in association with it ; and chromate of iron and 

 statactitic iron ore are found embedded in the dykes. In 



