602 



MR. J. J. LISTER ON THE GEOLOGY 



The most striking feature of the formation is the existence of well 

 marked terraces on the lower slopes. 



The terrace rr, as above stated, extends along the whole length of 

 the western side of the island, at an elevation of about 250 to 3G5 

 feet above sea-level. 



The outer, western border of the terrace is for a great part of its 

 length higher than the interior. Beginning at the northern end, 

 we find the terrace forming a narrow band, so narrow that it makes 

 only a slight interruption in the sloping side of the island. To the 

 south it gradually widens out, being at first level from side to side, 

 but soon the interior becomes depressed below the margin. The 

 depression is greatest at one-third of the length of the island from 

 north to south. Here the margin is about 65 feet higher than the 

 interior. As we advance southward the depression of the interior 

 becomes less marked, until at the junction of the middle and 

 southern thirds of the length of the island the terrace is again 

 level, and remains so to the southern end. Passing across the 

 terrace from east to west, in the region of the depression we 

 descend a very gradual slope to near the outer border. From the 

 lowest part the ground rises to the margin of the terrace, in most 

 places by a gradual ascent, but at one point the rise is abrupt. 

 Opposite the town of Ohunua there is a gap in the high margin, 

 the bottom of which is at the same level as the depressed inner 

 part of the terrace. Through the gap there runs a steep-sided 

 ravine, cut in the limestone rock ; it is formed by the junction of 

 two of the overflow channels of the streams of the upper part of the 

 island, and there is water in it only after heavy rains. Having 

 passed the gap the ravine pursues a straight course down the 

 sloping side of the island to the sea, and at its mouth there is a 

 break in the reef and an anchorage for small vessels. 



On the margin of the terrace to the south of the gap the lime- 

 stone rock forms projecting masses, and in some of these definite 

 Astrcea-like coral structure is to be seen. Other specimens present 

 a homogeneous structure to the naked eye. Dr. Murray has ex- 

 amined sections of these*, and finds that they are "chiefly made 

 up of calcareous algse, together with fragments of coral, molluscs, 

 echinoderms, and foraminifera " f. He concludes from the cha- 

 racter of the organisms that the deposit was " formed in quite 

 shallow water." 



With regard to the peculiar conformation of the terrace, it appears 

 that the depression in the interior must either have existed at the 

 time that the terrace was elevated above sea-level, or have been 

 excavated since by the denuding action of rain or streams. 



Slide No. 1271. 



Among the foraminifera the following kinds were recognized : — 



Miliolina, sp. 

 Orhitolites duplex {?).. 

 Textularia trocJtus (d'Orb.). 

 Globiycrina buUoides and Gl. rubra (?). 



Planorbulina larvata (P. & J.). 

 Carpenferia monticularis (Carter). 

 Polj/trema miniacenm (Linn.). 

 Calcarina hispida (Brady). 



