4 ME. J. S. GAEDINER ON THE GEOLOGY OF K0TTJ3IA. [Feb. 1 898, 



about 5 miles long by 2g broad, and the heights of its hills Yary up to 

 860 feet. Along it the hills run in two lines, but to the east they 

 are closed by Satarua, so that they appear to have a U-shape with 

 a deep and, in places, very broad valley between, right up the 

 centre. Eound this, everywhere between the hills is a ridge with a 

 general height of a little over 100 feet, and a minimum of about 

 60 feet between Satarua and Hof. On their outer faces, towards 

 the sea, are extensive beach-sand deposits, especially to the north at 

 Oinafa and to the south at ISToatau and Pepji, while the flat land 

 between the two ends is similarly formed. On the reef, which is 

 fringing, with in places an approach to the barrier class, are several 

 islets with a gradual slope towards the land, but precipitous cliffs to 

 the sea. 



On an examination of this U-shaped range of hills, which appear 

 wonderfully uniform in height, they are found to have a flat 

 summit with a central depression of varying depth, or to run up 

 into a ridge. In both cases the angle of slope for the last 200 to 

 300 feet varies from 30° to 55°. This appearance is further often 

 accentuated by the vegetation : large forest-timber on the summits 

 and slopes of the first, but on the second planted land, sometimes 

 right across the ridge itself. 



Satarua, the most easterlj'' of this range, combines to some 

 extent the characters of both classes. Prom it to the north-east run 

 out into the sea four prominent points, all of porous lava. Behind 

 these the land rises with a slope of 1 in 30 to 1 in 20 for about 

 ^ mile, covered for the most part with rough, hard, vesicular 

 lava, often in loose blocks, with very little earth. The rise then 

 gradually increases to 1 in 6, or 4, for the next 300 feet, the rough 

 lava being gradually more and more covered with earth. The 

 steepness of the land continually increases, only small blocks of lava 

 are to be found for the next 50 to 100 feet, and then there is an 

 abrupt rise for the last 250 or 200 feet at an angle measured at 

 41° to 44°, the height of the mountain being a little over 700 feet. 

 On the top is a crater 150 feet broad by 40 deep. The slopes 

 into it are steeper than the external slope, while the bottom is 

 perfectly flat, and indeed, as many of these craters do, gives evidence 

 of having at some previous time been planted for food. The rim is 

 about 10 yards broad, and consists, with both of the slopes, of loose 

 earth, with only small lava-blocks here and there. From the rim 

 of the crater there extends to the south-west a ridge, sloping down- 

 ward, but undulating, about 150 yards long by 15 to 25 yards broad. 

 Beyond it the slope again plunges down at an angle of about 40°, 

 and the general character is the same. 



This bare low-lying stretch of lava at the base of the hill, 

 mentioned above, with a low angle of rise, passing into a rich and 

 highly arable soil, is very characteristic of aU the volcanic hills of 

 the island. It usually presents an extremely rugged and rough, black 

 appearance, sometimes covered with loose, large blocks, but more 

 often completely bare. 



Of the other hiUs in the range, Mafoa is a cone wdth a crater on 



