1835.] Geological Sketch of the Neilgherries. 431 



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 lamina?, 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 Kaiti 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 thfn 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. 



Examining some of these masses, we see evidently that, in many of 

 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 laminae. 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 laminae ; but this dyke did not penetrate into the 

 upper remaining portion of the laminse, which was incumbent on it. 

 This dyke continued evidently under the remaining portion of this 

 laminae in the nucleus of the rock. 



Going from Ootacamund towards Nundiwatum, 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 

 3 k 2 



