124 GREAT SERPENTINE BELT OF NEW SOUTH WALES, iv., 



lavas in Savaii as follows{8) : — "An ovoid mass of lava still in com- 

 munication with the source of supply, and having its surface, 

 though still red-hot, reduced to a pasty condition, would be seen to 

 swell or crack into a sort of bud with a narrow neck like a prickly 

 pear on a cactus, and this would rapidly increase in heat, mobility, 

 and size, till it either became a lobe as large as a sack or pillow, 

 like the others, or perhaps stopped short at the size of an Indian 

 club or large Florence flask. Sometimes the neck supplying the 

 new lobe would be several feet long and as thick as a man's arm 

 before it would expand into a full-sized lobe; more commonly it 

 would be short, so that the fresh-formed lobes were heaped 

 together." Sundius accepts this as the process by which the 

 pillow-lavas were made in the pre-Cambrian rocks of Lappland, 

 but suggests that the pressure of the moving lava may break off 

 and separate the pillows from one another : this would account 

 for the rarity of connecting tubes between the pillows in the 

 lavas he describes. Daly, in his recent work (9), compares the 

 production of these lava-ellipsoids to the formation of the "sphe- 

 roidal state " in water. Sundius notes that the effect must 

 depend on the possession by the magma of a definite degree of 

 viscosity, and finds in this the explanation of the association of 

 pillowy and non-pillowy lavas. Mr. Harker has pointed out(lO) 

 that there is only a slight difference between the conditions of 

 injection of lava into the loose muds of sea-floor, and an outflow 

 of lava over the sea-floor, which is but the injection of magma 

 between the soft muds and the overlying water.* The difference 

 is naturally to be found in the slower cooling of the lava in the 

 former case owing to the blanketing action of the muds. It 

 seems quite probable that a flow with typically pillowy surface 

 mav show an intrusive contact with the mud-surface on which it 

 rests, and such may be the case in parts of the Nundle district. 

 While, in many instances, pillow-structure is a feature of deep-sea 

 marine flows, as is shown by the fine-grained nature of the sedi- 

 ments with which they are associated, it is clear, from Tempest 

 Anderson's observations, that it cannot be confined to such situa- 



* Compare F. vou WolflF. Der Vulkauismus (Stuttgart, 1913), pp.252 

 and 255. 



