428 Geological Sketch of the NeUgherries. [Aug. 



I never saw it, except in the form of erratic blocks, in the low valleys 

 (No. 39). In those places it has the usual appearance of immense 

 masses split both by vertical and by horizontal fissures, into columnar 

 or prismatic figures ; they, however, no where assume the tor-like 

 appearance so common in the granitic hills in other parts of India. 

 The granite occasionally is of a dull, yellowish brown colour, owing 

 to the felspar, which assumes that tint, resembling in that state the 

 feuille morte of the French. Doctor Hardy has remarked the same 

 change of colour in the granite of Mewar. 



The other species of granite, found always associated with the former, 

 is the pegmatite (No. 40), a rock composed of only two minerals, 

 felspar and quartz. The places where I have found this rock in situ 

 are marked in the map : it is a variety of the graphic granite ; in aspect 

 very different from the same rock found in other parts of Southern 

 India, in which the quartz is regularly crystallized, and the felspar in 

 long slender crystals, of a pale flesh colour. 



In the variety of this rock on the Neilgherries, the felspar is milk- 

 white, lamellar ; but not in regular prismatic crystals : the quartz is 

 occasionally of a smoky colour or bluish ; and in angular pieces, this 

 colour is sometimes so deep as to appear nearly black. In some of the 

 masses are occasionally seen a few garnets, or a little hornblende ; 

 but in general, the rock is exclusively composed of the two minerals, 

 felspar and quartz*. 



Of this rock some erratic blocks are seen in the valleys, at the foot 

 of those hills, the summits of which contain it in situ : this is the case 

 in the Kaiti valley, whither many of these boulders have been pro- 

 bably hurled down either from the summit of Dodabetta, or from the 

 Kaiti peak, where pegmatite is found. 



It is undoubtedly from the decomposition of these masses, that the 

 porcelain earth described in the beginning of this sketch, arises. 

 By comparing the specimens of the one with those of the other, the 

 identity of the two is established. 



The sienitic granite varies in the proportion of its component 

 minerals, and therefore in appearance ; sometimes approaching diabase 

 (primitive greenstone), and at others, granite (No. 4l£). It almost 

 always contains garnets as one of the minerals composing it ; and 

 when this mineral is abundant in the rock, the quartz diminishes in 

 proportion. In the Dodabetta group, I have remarked in some 



* This species of granite seems to be very common in many parts of India, 

 — Dr. Hardy appears to describe it in many localities, in his sketch of the 

 Geology of Central India. Many of the blocks jutting up in the plain between 

 Palaveram and Madras, such as that near the Race Course, are all pegmatite. 



