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Memoir on the Geology of the 



[Oct. 



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. 35). The masses 

 under the village, exfoliate into concentric lamina?, in which are some 

 needle-shaped shining crystals, probably of augite (No. 86). 



Another enormous dyke of this rock is seen in the chain of hills 

 which connects Doodabetta with Kaitee 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 granu- 

 lar and shining, somewhat approaching primary greenstone. 



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 overlay 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. 87). On looking at the surface of the blocks level 

 with the soil, we see it divided into irregular portions by the ramifica- 

 tions 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 peg- 

 matite exfoliating in thick laminee. Portions of one of these had been 

 removed, either by disintegration or otherwise; the remainder (perhaps 

 a foot thick) was still overlaying 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 laminee, which was incumbent on it. This dyke conti- 

 nued evidently under the remaining portion of this laminee in the 

 nucleus of the rock. 



Basaltic Dykes — Neddiwattum Road.-— About two miles from Ootaca- 

 mund along the Neddiwattum road, there is a small rivulet, close to the 

 road, the first we meet in this direction. A basaltic dyke, like a ledge, 

 half in the water and half out, is seen in an oblique position, N. E. 

 and S. W. dipping north. I shall term this the rivulet dyke, to dis- 



