xxii VOLCANIC AGGLOMERATES 315 



which these accumulations occurred. They are dealt with at some 

 length in the general description of each district and only a brief 

 reference can be made to some of their indications here. 



The testimony supplied by the interesting exposures on the 

 slopes of Mount Thambeyu (page 178) goes to show that after the 

 deposition of the foraminiferous tuffs and clays the stage of the 

 agglomerates was ushered in gradually. The tuffs increased in 

 coarseness, and afterwards they were covered up with an 

 agglomerate formed of blocks at first only one or two inches in size, 

 but afterwards of larger dimensions. . . . Curious evidence is 

 afforded by the agglomerates of Mount Vungalei (page 213), where 

 two beds of palagonite-tuff, at elevations of 900 and 1,700 feet, mark 

 two pauses in the accumulation of the agglomerates. In each case 

 the pause was introduced by the gradual decrease of the agglomer- 

 ates which gave place by gradation to the tuffs. In each case also 

 the pause was followed by a sudden renewal of the deposition of 

 agglomerates. 



With reference to the maximum thickness of these deposits, it 

 would appear that on the slopes of the Korotini Range this amounts 

 to some hundreds of feet, if we also include the tuff-agglomerates. 

 Their origin is to be attributed partly to eruptions and partly to 

 marine erosion. The two agencies although often associated were 

 in their turns predominant in their different phases, and it is not too 

 much to suppose that the agglomerates without arrangement, with 

 scanty matrix, and composed of scoriaceous blocks, belong more to 

 an eruptive period, and that those with abundant tufaceous matrix 

 and sorted blocks are mainly the product of marine erosion. In 

 either case the deposition was submarine. 



But the history of these agglomerates and of their associated 

 foraminiferous tuffs and clays must of necessity be a complicated 

 one, since they indicate a minimum emergence of 2,500 feet. Their 

 accumulation first began when a number of vents, in linear arrange- 

 ment, were striving to raise their heads above the surface of the sea. 

 It was continued after the waves had ultimately worn the volcanic 

 islets down to below the sea-level, and the shoals became covered 

 over with submarine deposits. Again and again no doubt this 

 struggle between the eruptive agencies and the waves was renewed, 

 until at length the great emergence began, and probably from that 

 date the agency of marine erosion was predominant. 



When on the island of Stromboli I had presented for my 

 observation at least two modes of agglomerate-building under the 

 sea. There was the ordinary work of the marine erosion of the 



