CHAPTER VII 



DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL 

 FEATURES (continued) 



THE NDRANDRAMEA DISTRICT 



THIS hilly region of acid andesites is a continuation of the 

 mountainous backbone of the island, being separated from the 

 basaltic mountain of Seatura by the saddle formed by the Na 

 Savu table-land. These acid andesites exhibit in nearly all cases 

 a felsitic groundmass and phenocrysts of plagioclase and rhombic 

 pyroxene; whilst many of them are characterised by brown horn- 

 blende more or less pseudomorphosed in the manner described on 

 page 306, and a few display porphyritic quartz. Although these 

 rocks have a common facies, they vary considerably among them- 

 selves ; and it is difficult to find a term that would strictly include 

 them all. A general description of their characters is given in the 

 chapter on the Acid Andesites. 



In this interesting region a number of hills or mountains formed 

 in mass of acid andesites rise up abruptly without any regular 

 arrangement within an area measuring 5 by. 6 miles, and elevated 

 00 to 1,000 feet above the sea. Of these hills, thirteen in all, 

 nine range in height between 1,600 and 2,500 feet above the sea, 

 none of the others rising less than 1,000 feet above that level. But 

 the actual height of each hill above the country at its base is much 

 less than this. The height of the hill-mass, in five or six of the 

 largest, ranges between 900 and 1,200 feet, whilst in the smaller 

 hills it varies between 400 and 800 feet. (See accompanying plan.) 



These hills have sometimes a rounded profile, when their summits 

 are usually wooded. Others again terminate in conical bare rocky 

 peaks, either pointed or truncated. They have often precipitous 

 slopes and display vertical cliff-faces high up their sides. Their 



