1836.] 



2V 'eelgherries and Koondahs. 



267 



visible of it, and its composition is the following : lamellar garnets, 

 some of them half an inch in diameter, which, as I have said, have the 

 appearance of the dodecahedral species of that mineral— cinnamon- 

 stone, or essonite ? (No. 81). Their number is such, that entire por- 

 tions of the rock are formed almost exclusively of them. Next to this 

 mineral in quantity is hornblende, in well-formed large crystals, lami- 

 nar in its structure, and of a shining aspect; to these is added a small 

 quantity of a granular grey coloured felspar, and a few plates of 

 mica (No. 82). These minerals are not uniformly disseminated through 

 the substance of the rock, particularly the cinnamon-stone and the 

 hornblende, which are contained in large separate crystals, imbedded 

 in a paste, composed of compact felspar and hornblende; and it is to 

 be remarked, that the presence of the four minerals is not always con* 

 stant in the rock ; since in some portions it contains hardly any other 

 mineral than foliated, brilliant hornblende (No. 83). 



Of all these minerals it seems that the cinnamon-stone is the most 

 liable to decompose, or disintegrate ; since we see, in some parts of the 

 surface of the mass, small cavities, in consequence of the falling out of 

 the disintegrated crystals of this mineral. This rock is very compact, 

 exceedingly heavy and takes a brilliant polish. 



These are all the rocks I have met with on the Neelgherries, 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, 

 overlaying 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 Koonoor pass. Not more than 

 a mile from the bridge down the pass, and just below the village of 

 Koonoor, 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 into 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 di- 

 vided into well marked prisms above the granite (No. 84). 



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 



