xv NAT AS A BAY 209 



and probably submarine are here displayed together with basaltic 

 andesites. 



(d) The coast between Natasa Bay and the vicinity of Tawaki. 

 This extensive stretch of sea-border, nearly 15 miles in length, is 

 characterised by hilly spurs and long intervening low-lying tracts. 

 The prevailing rocks exposed are tuff-clays, somewhat hard and 

 altered, and coarser basic tuffs sometimes calcareous and overlying 

 the former. These sedimentary deposits, which are evidently 

 submarine, are often bedded and have a fairly constant dip over 

 most of this region of 10 to 15 degrees to N.W. or W.N.W. They 

 are frequently pierced by dykes, 6 to 10 feet thick, of compact 

 basic rocks. A specimen of one of these dyke-rocks from between 

 Natasa and Vatu-karoa is a doleritic basalt with scanty olivine 

 (sp. gr. 2'Si) 1 ; but the rock of the dykes east of Vatu-karoa is less 

 basic (sp. gr. 272), and may be described as an augite-andesite 2 

 with a doleritic structure in part disguised by alteration. Between 

 Natasa and Sangani there is a remarkable exposure of an intrusive 

 opaque white rhyolitic rock associated with altered tuffs. This 

 rock, which has undergone some degree of alteration, is described 

 on page 311. It is the only indication of the vicinity of a region 

 of acid rocks that I came upon on this tract of coast. It probably, 

 if traced inland, would be found connected with the district of acid 

 rocks. In following along the coast, however, towards Undu Point, 

 the region of acid rocks is not reached until within 2 or 3 miles 

 west of Tawaki. Reference should be made here to two hot springs 

 that, as described on page 33, rise up on the coast at Natuvu, a 

 little east of Lakemba. 



THE INLAND MOUNTAINOUS REGION BETWEEN THE EASTERN 

 FOOT OF THE MOUNT THURSTON RANGE AND THE VICINITY 



OF TAWAKI 



This inland region corresponds for the most part to the tract 

 of coast before described between Vuinandi and the vicinity of 

 Tawaki. We have here a very much broken area traversed in a 

 northerly and southerly direction by mountain-ridges and penetrated 

 in places on the north side by prolongations of the Wainikoro and 

 Kalikoso plains. The two loftiest summits, the Ndoendamu and 



1 It belongs to genus 37 of the olivine class. The felspar-lathes average 

 0-2 mm. in length, and there is a little altered interstitial glass. 



2 It is referred to genus 16, species D, of the augite-andesites. The felspar- 

 lathes have an average length of '3 mm. 



P 



