5° 



A NATURALIST IN THE PACIFIC chap. 



of the volcanic activity that began with some violence, as shown by 

 the characters of the lowest bed. Now another outbreak occurred, 

 and overlying the clay-like bed we find a coarse tuff made up of 

 fragments 2 to 5 millimetres across, and approaching in texture and 

 appearance a subaerial tuff, but in other respects similar to those 

 below it. It is the last and uppermost of this series of acid tuffs, 

 and with it terminates an interesting record of the past in this 

 region, the chief features of which may thus be summarised. 



A prolonged period of quiet deposition of submarine basic tuffs, 

 the products partly of marine erosion and partly of distant 

 eruptions, was abruptly followed by the outbreak of a neighbouring 

 vent during which tuffs formed of the debris of acid andesites were 

 deposited. The gradual decrease in the degree of activity is 

 plainly shown in the gradual diminution in size of these tuffs, until 

 they acquire the fineness of a clay. Then another burst of activity 

 from the same vent or vents occurred, and the record ends. Since 

 that time there has been apparently an upheaval to an elevation of 

 300 feet above the sea. As, however, the beds are quite un- 

 disturbed, the emergence may have been due to the lowering of 

 the sea-level, a subject which is discussed in Chapter XXVII. 



Coast between Wailea Bay and Lekutu. — The hills 

 here often approach the coast, their spurs running down to the 

 beach. In the low range, 250 to 300 feet high, east of Wailea Bay, 

 are exposed palagonite-tuffs dipping gently north-east and com- 

 posed of fragments of a vacuolar basic glass, more or less palagoni- 

 tised, and of minerals (plagioclase, etc.) not exceeding 2 mm. in 

 size. These deposits are apparently non-calcareous and show no 



organic remains. 



Farther along the coast towards Nativi basic tuffs and agglo- 

 merates appear at the surface ; but the underlying rock, exposed 

 in position in the stream-courses and prevailing along much of the 

 sea-border to Nativi and a mile or so beyond, is a vesicular semi- 

 ophitic basaltic andesite with coarse doleritic texture and containing 

 much interstitial smoky glass. (It belongs to the non-porphyritic 

 group of genus 9 of the augite-andesites described on page 273.) 

 Such rocks evidently represent ancient flows. They give place as 

 one proceeds east to porphyritic semi-ophitic doleritic rocks of the 

 same genus and to semi-vitreous basic rocks. About half a mile west 

 of Nukunase a vesicular doleritic basaltic andesite forms a spur 

 protruding at the coast. It is semi-ophitic and contains in the 

 smoky glass of the groundmass little irregular cavities filled with 

 a yellowish residual magma like palagonite in character. (It is 



