344 A NATURALIST IN THE PACIFIC chap. 



successful production of palagonite lies. In both these experiments 

 some of the conditions of a submarine flow have been reproduced. 



Whilst Rosenbusch established the true character of palagonite 

 as the product of a peculiar alteration of a basic glass, Renard 

 pointed out the conditions under which it was most typically and 

 in greatest abundance formed. But Bunsen was happy in his 

 suggestion that palagonite-tuffs are submarine deposits derived 

 from the breaking up of previously formed palagonite masses. 

 The question thus resolves itself into one concerning the conditions 

 of submarine eruptions and the behaviour during consolidation of 

 a submarine basaltic flow. In the nature of things the field of 

 investigation is mainly restricted to the examination of ancient 

 submarine basaltic flows that have been raised above the sea. 



A remarkable series of beds exposed in a stream-course below 

 the Nandua tea-estate may be here described in connection with 

 the question of the origin of palagonite formations. As observed 

 on page 86, this locality lies on the flanks of a basaltic plateau, 

 which are incrusted with recent submarine deposits. A pteropod- 

 ooze, containing also the tests of large and small foraminifera and 

 the shells of small bivalves, is displayed on the sides of the 

 stream-course for the first 1 50 feet of the descent. Below this, as 

 shown in the diagram, is a declivity with a drop of 60 or 70 feet 

 where there is a waterfall. Horizontal beds of the pteropod-ooze 

 rock are exposed in the upper-third of this declivity ; but below, 

 they pass into a chocolate-coloured marl-like deposit also horizon- 

 tally bedded, and sometimes having a banded appearance from the 

 alternation of layers of different degrees of fineness. This rock 

 contains S or 6 per cent, of carbonate of lime and incloses a few 

 scattered tests of minute foraminifera of the " Globigerina " and 

 " Nodosaria " types. In the slide the rock appears to be of massive 

 palagonite inclosing a few felspar-lathes 'i to "3 mm. in length, and 

 exhibiting a zeolite and calcite in the crevices and cracks. But it 

 was not until I had discovered the tests of the foraminifera and 

 had observed some fragments of larger crystals of plagioclase and 

 a little detritus of a semi-vitreous basaltic rock that its clastic 

 character was disclosed. The palagonite change has here to a 

 great extent disguised the character of the deposit. 



This palagonite-marl formation is 20 or 30 feet in thickness. 

 It passed downward into a reddish-brown rubbly unstratified rock 

 which falls to pieces in one's hands, breaking up into little cube- 

 like masses an inch or two across. These masses display in 

 their interior a radiate prismatic structure ; but after drying they 



