48 LA TOUCHEr GEOLOGY OF WESTERN RAJFUIANA. 



in a northerly direction. Flow-structure is well developed in this rock 

 and is very conspicuous on the Weathered surfaces. The edges of the 

 flows present a steep scarped face to the south and exhibit a well 

 defined columnar jointing, at right angles to the surface of the flows. 

 The rhyolites rest upon a series of buff coloured felsitic tuffs and ash 

 beds, which are exposed on the slopes of the hills below the scarps, and 

 also dip slightly towards the north. Some of these beds are distinctly 

 fragmental, the fragments being imbedded in a glassy felsitic paste. 

 Others have a bright green colour mottled with specks of red haematite 

 and are apparently largely composed of chloritic mud. 



The large hills, rising to 902 feet, about four miles to the south-west 

 of Korna, are mainly composed of strongly porphyritic rhyolite, with a 

 dark purplish colour. A small knoll at the northern end of the group 

 consists of compact glassy rhyolite with well developed flow-structure, 

 containing fragments, sometimes up to three or four inches in diameter, 

 of a previously consolidated flow of a similar rock, but darker in colour. 



A short distance further to the south-west, in the neighbourhood of 

 Nagona, an interesting series of rocks is exposed. The large hill, 

 937 feet high, immediately to the south of the village, is composed of a 

 glassy looking rhyolite, which splits up easily along vertical plains, which 

 are seen to be lines of flow, causing the rock to be almost as fissile as 

 ordinary slate. On the top of the hill these divisional planes are seen 

 in plan to pursue a wavy direction, generally about north-west to 

 south-east and sometimes flowing round an included mass of more # 

 massive porphyritic rock. In the surrounding hills patches of a similar 

 fissile rock are frequently met with, among the nearly horizontal 

 flows of more porphyritic rhyolite of which the main mass of the hills 

 is composed, and rise through the latter after the manner of an 

 intrusive dyke. There is nothing to indicate that there has been any 

 great disturbance of the rocks since they were poured out, or that the 

 fissile rock was originally horizontal ; and it seems therefore very 

 probable that the vertical character of the flow-structure is due to 

 ( 43 ) 



