1836.] 



between Madras and the Neilgherries. 



23 



bearers should halt in the road till day-light, to enable me to satisfy my 

 wishes, and then join the party at MacDonald's choultry. 

 . I reached the magnesite at midnight, and remained in the road till 

 day-light, when I got up and began my examination. About five miles 

 N. W. of Salem, the schistous diorite, which we have seen forming all 

 the hills in this neighbourhood, is intersected by numerous veins of 

 magnesite, of different thickness, and crossing each other in all direc- 

 tions, so as to make an intricate net-work in the rock (No. 79). 



The masses containing the magnesite have hardly any elevation 

 above the soil, and the area, occupied by this formation, may have about 

 fifteen miles circumference, the surface being undulated with a few 

 knolls and nullahs. 



Nearly all the veins of magnesite are vertical, and the only ones I 

 saw in an horizontal position were those in the banks of the nullahs. 

 These veins vary in thickness from a few lines to three or four inches, 

 and they are not uniform in their dimensions, sometimes thinning, and 

 at others thickening, along their course. 



Generally speaking the rock intersected by the magnesite is decom- 

 posed into an ophitic stone (No. 80), sometimes quite friable and pow- 

 dery ; at others it resembles decomposed wacke (No. 81). Those 

 masses of hornblende slate which have either very liitle magnesite or 

 none at all, maintain their crystalline structure. In more than one 

 block, between the magnesitic veins and the rock, I found thin veins of 

 asbestos, of an indurated earthy structure, and in some other masses^ 

 instead of it, talc slate and nephrite (No. 82). 



The outgoings of these magnesitic veins, in general, are rough and 

 bristled with numerous sharp points ; but many others, particularly 

 the loose pieces, have a mammillated, botryoidal, or cauliflower-like, 

 surface. In more than one of these last mentioned pieces the surface 

 is excavated by little furrows (No. 83). These veins are nearly all 

 formed of simple magnesite ; there are, however, some in which the 

 magnesite is contained in a breccioide mixture, its angular pieces being 

 imbedded in a pale red kind of cement (No. 84). 



This magnesite is extremely heavy and compact, so as to strike fire 

 with a hammer ; of course I mean the most compact kind. Its fracture is 

 eemi-conchoidal, earthy, and has the dull waxy appearance of some of 

 the varieties of the alpine lime-stone, except that it possesses greater 

 whiteness. It effervesces slightly with acids. 



This mineral attracted the attention of European gentlemen, who first 

 visited the place, particularly Dr. MacLeod, and others, who accurately 

 examined and analyzed the magnesite, and made numerous experiment?, 

 not only regarding its medical qualities, but also as to its utility as a 

 cement, particularly for works constructed under water. 



Judging from- the few trials I witnessed at Madras with the magnc- 



