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 milkwhite, 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 Kaití valley, whither many of these boulders have been probably hurled down either from the summit of Dodabetta, or from the Kaití 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. 41). 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.

places the garnets, instead of being either amorphous, or in angular crystallized pieces, assume the granular form, resembling colophonite ; in which case, the rock containing it assumes a stratified appearance (No. 41).

The colophonite is composed of granular garnets, greenish hornblende, a little felspar, and less quartz. I have seen in your museum a specimen sent by STRÜVE from Norway, very much like the specimen I now send. The geological position of this rock, which I have found in one or two localities only, is the following. It is to be seen clearly in the ravine just above the high road going to Kúnúr, and close to the public bungalow of Kaití. Two huge masses of a black-looking unstratified rock are seen overlying three strata of a different rock. The upper and unstratified mass is a hornblende porphyry, which passes into sienitic granite. It is very nearly similar to the rock of the same composition I have mentioned as flanking the hæmatitic iron ore, behind Mantu village (No. 42). I have found precisely the same rock overlying the sienitic porphyry of the Garabunda pass, in the Northern Circars. Its hornblende is shining and lamellar, and is the most abundant of the component minerals; the garnets appear to be surrounded by a white powdery opaque felspar, they themselves half decomposed. Below this half-rounded mass is a stratum of a felspar rock, with a very little quartz and hornblende decomposing (No. 43). The thickness of this stratum, which is uniform, does not exceed a few inches; another, but thicker stratum of a granitic rock, lies under, and conformable to the above, being composed of reddish felspar, some garnets, little quartz, and mica; the passage from one rock to the other is sudden, decided, and well marked. Under this, and conformable to it, is a stratum of a rock almost entirely composed of hornblende and granular garnets: this is the lowest of the rocks seen; it becomes harder as it descends, when it assumes the appearance of colophonitic hornblende rock.

This lower rock appears stratified, and besides the seams of stratification, it has some fissures, perpendicular to them; so dividing the stone into prismatic portions. On account of the thick stratum of soil at the foot of the rock, I could not ascertain whether the last-mentioned was the lowermost rock. I must here remark, that the appearance of the two rocks immediately under the hornblende porphyry was that of a decomposing stone, as if from the action of fire.

The rock which prevails in the Kaití range, as well as in other places, is the one which abounds both with hornblende and amorphous garnets. These last sometimes are of a large size, and not

dispersed through the rock, but, as it were, in nests (No. 44). This rock is very like the specimen in your museum from Norway, marked " large garnets in hornblende." Indeed, I think that there is great analogy between the sienite zirconienne of Norway and this rock of the Neilgherries (No. 45). I remarked in one place of the Dodabetta group some veins containing quartz and garnets; the last in the granular or resinitic form (No. 46).

Before dismissing the subject of the hornblende rock, I must remark, that although this primitive greenstone is occasionally seen on the summit of some hills, in general it occupies the declivities or the lowest parts of them; and it often assumes a brilliant, laminar crystallization, being then exclusively formed of hornblende (No. 47).

I have seen it passing into hornblende slate at the foot of the Neilgherries, at the bottom of the Kúnúr pass. Here its strata dip to the east, and I am informed, that the same stratified rock is found at the foot of the same group of hills, to the west, the strata in that place dipping west. It is in those places that this rock occasionally passes into sienitic gneiss.

These are all the rocks I have met on the Neilgherries, of which their extensive plateau is formed, and the relative position of which can often only be surmised, on account of the thick covering of soil, and of red earth, which conceals the rock generally.

I must in the last place notice the numerous basaltic dykes which burst up through all these rocks indiscriminately, without however overlying them, except in one situation; and even there the basalt only forms a small ridge, flanked by the fundamental rock.

I shall describe briefly those places where I have had opportunity of examining this rock; and first, that in the Kúnúr pass. Not more than a mile from the bridge down the pass, and just below the village of Kúnúr, in the road, many of the blocks which have been blasted, are traversed by a dyke of basalt. In the little ravine close to the road, the dyke is seen in situ through the masses of granite in the jungle. This dyke divides in two or three branches, inclosing betwixt them the granite; then it is seen continuing in a north direction, till close to the huts of the village. The projecting masses through the soil indicate the direction of the thick dyke, which in a place near the road is divided in well marked prisms above the granite (No. 48).

This basalt is very compact; has a dull, even fracture; but in one portion of the dyke, I had the opportunity of observing, that the part which was in contact with the granite had the appearance of a crystalline hornblende, which passed into compact hard basalt towards the centre of the dyke. I also remarked, that where the dyke.

was in contact with the granite, the basalt was projecting in a small ridge, which was divided into small prisms, as if the consequence of sudden refrigeration, and subsequent contraction (No. 49). The masses under the village, exfoliate into concentric laminæ, in which are some needle-shaped shining crystals, probably of augite (No. 50). Another enormous dyke of this rock is seen in the chain of hills which connects Dodabetta with Kaití pass. The summit of the hill, which is between those two mountains, is formed of basalt in huge masses, some of which affect the prismatic figure. In general the large blocks are not so compact as the thin ramifications of the dyke traversing the rock, but the hornblende in the former is nearly granular and shining, somewhat approaching primary green

stone.

On the eastern and western slopes of this little ridge, the rock, of which the hill seems formed, is seen in huge projecting masses, so that the basalt does not appear to overlie the rock, but to have burst through it, vertically, in the centre of the ridge.

Going along the ridge from N. to S. after passing a little hollow, we ascend the hill, the summit of which is basaltic. The first intimation we have of the existence of this rock, is seeing many of the blocks of pegmatite traversed in all directions by a reticulated infiltration of basaltic matter (No. 51). On looking at the surface of the blocks level with the soil, we see it divided in irregular portions by the ramifications of the dyke.

of

Examining some of these masses, we see evidently that, in many them, the thickness of the dyke diminishes as it proceeds upwardly, and therefore showing the injection of the basalt to have taken place from below. The following appearance exhibited by one of the blocks, shows clearly this direction of the basalt. It is a large mass of pegmatite exfoliating in thick laminæ. Portions of one of these had been removed, either by disintegration or otherwise; the remainder (perhaps a foot thick,) was still overlying the nucleus of the rock, which was nearly level with the soil. A basaltic dyke, an inch thick, was observed in the nucleus of the rock, which had been denuded of a portion of the lamina; but this dyke did not penetrate into the upper remaining portion of the lamina, which was incumbent on it. This dyke continued evidently under the remaining portion of this laminæ in the nucleus of the rock.

Going from Ootacamund towards Nundi watum, along the new road, after about three miles, we meet with two basaltic dykes close to the road.

The first is seen near a small stream, like a ledge projecting at an

angle with the horizon, and the basset of which is hardly a foot above the soil. Its dip is west; its direction nearly N. and S.; and it is seen continued along the declivity of the hill for some hundred yards. It is traversed by fissures in different directions, giving the pieces a prismatic appearance. Proceeding N. we see in the next hill another and thicker dyke, with precisely the same direction as the former.

The basalt in this place traverses sienitic granite, and it is seen clearly on the side of the road. The pieces of all shapes, as prisms, cubes, rhombs, are strewed below the newly cut road. Above the road, the projecting masses of sienitic granite are traversed by innumerable ramifications of the dyke, enclosing between them pieces and masses of the fundamental rock (No. 52).

The same observation made when speaking of the Kaití dyke, is also applicable to this: the small basaltic veins have a compact, and dull texture, while the body of the dyke itself has a granular-like structure, and somewhat shining (No. 53).

In some of the Kúnda mountains, as that of the Avaláche, I also noticed some of these basaltic dykes; and judging from the numerous rounded blocks and pieces of basalt seen in the bed, and in the banks of the river, which descends from the hills N. of the Avaláche, basalt must be very common in that group.

Basaltic dykes are not rare in those places, which I have had an opportunity of visiting in the plains of India. I have seen them through granite and gneiss in Mysore; through porphyry, near the erratic hill of Adamanacotta; through hornblende slate, near Mottipollium; through porphyry, near Garabunda (Northern Circars), and in many other places. Are these dykes the fissures through which the enormous mass of trap, overlying most of the rocks of the peninsula, burst up? and which, subsequent events and revolutions having removed, the vents only through which it was forced up remain to be seen?

It is a well-ascertained fact that the structure, if not the nature, of rocks in contact with the basaltic dykes, is often greatly changed or modified. I saw nothing of this alteration in the rocks close to the dykes I have been describing. The specimen I send, shews no other change, except a slight diminution of cohesion among the composing minerals, and that not in a very marked manner, nor in every locality.

The above described are the rocks I had an opportunity of examining on the Neilgherries, having met none of the secondary, and much less of the tertiary class. It would appear from this, that the eleva. tion of this plateau, and probably of the whole chain of the western