142 A NATURALIST IN THE PACIFIC chap. 



the blocks, which are formed of a semi-vitreous basaltic andesite 

 of the augite class, being not generally more than 3 or 4 inches 

 across. These blocks, which are rounded on the outer exposed 

 side and angular on the imbedded side, are inclosed in a hard, 

 probably calcareous matrix. The whole face of the cliff has the 

 appearance of having been worn smooth by attrition, and there are 

 not to be observed the projecting blocks from its surface which are 

 so characteristic of other agglomerate-cliffs. It shows no strati- 

 fication ; but at its base flush with the cliff-face are large masses of 

 a basic massive rock. But few portions of rock have been detached 

 from the cliff. However, I found in the midst of a huge fallen 

 fragment of the agglomerate a dyke-like mass of a basaltic andesite, 

 which differs chiefly from the rock forming the blocks of the 

 agglomerate in being more crystalline. This dyke must have been 

 about 15 feet thick. 



Having regard to these various features, I am inclined to 

 consider that this leaning cliff represents one side of a large fissure 

 in the agglomerates which was occupied by a dyke. Reference 

 has been above made to the fact that the agglomerates may be 

 seen overlying the tuffs farther down the slope, so that the 

 conditions favourable for landslips exist. I have shown on page 

 III that the origin of the Mbenutha cliffs where agglomerates lie 

 on clayey tuffs may be thus attributed to a landslip. In the case 

 of the Nangara-ravi cliffs, the occurrence of this fragment of a 

 large basaltic dyke is of some importance in connection with the 

 origin of the basic agglomerates of this locality. 



The top of the mountain-ridge is about 700 feet above Nangara 

 ravi, or 2,000 feet above the sea. The tuff's and agglomerates that 

 once existed here have been stripped off" to a great extent and the 

 deeper rocks of the range are in part exposed. The upper part of 

 this ridge (1,700 to 2,000 feet) is formed of a rubbly pitchstone 

 where a basic glass has been broken up and then consolidated, the 

 interstices being filled up with palagonite as described in other 

 cases on page 313. Though non-vesicular, it is just such a rock as 

 one would expect to find on the surface of a lava-flow or on the 

 sides of a dyke. 



The crest of the range is here only a narrow ridge. I followed 

 it along in a north-west direction, gradually ascending on the way, 

 and in time the rubbly pitchstone gave place to a hardened 

 palagonitic clay rock, which was observed as high as 2,300 feet. It 

 apparently contains a little lime, and probably was at one time 

 foraminiferous ; but it is now much affected by hydration. Soon 



