A THEORY 01^ BULBOUS BUDDING 649 



instance, as already noted, pillows formed on yielding mud or ooze will 

 sink into their bed and develop rounded outlines beneath that may be 

 indistinguishable, from the upper surface. Furthermore, pillows may 

 constitute any portion of a flow that is otherwise massive, and hence 

 massive lava may replace the ordinarily flat-bottomed pillows of the base 

 or the multidomical upper surface or both. 



5. SEPARATION OF INDIVIDUAL PILLOWS 



Each budding extrusion is a separate diminutive lava flow, and within 

 narrowly restricted limits subject to the same "accidents" as larger flows, 

 such as overlapping and interfering with one another. However, at the 

 time of their formation they are connected in irregular zigzag series, and 

 in some of the older flows numerous such connections are well preserved, 

 and many examples of pillows connected by necks to massive lava have 

 also been described (compare plate 18, figure 2, and plate 19, figure 1, 

 with plates 22 and 23). The slight connection of the pillows with each 

 other and with the parent mass is a point of weakness, however, that may 

 readily be severed by contraction while cooling or by slight subsequent 

 warping or other movement, leaving the individuals wholly isolated. 



The falling away of pendulous ellipsoidal masses as the lava slowly 

 drops over a clifl, as observed by Green in Hawaii, may also produce 

 separate individuals if their outer crusts become sufficiently hardened to 

 prevent the welding of the masses together. This condition would prob- 

 ably obtain wherever the masses fall into water, although under favorable 

 conditions of temperature and rate of flow the presence of water would 

 not be necessary. 



6. INTERSPHEROIDAL CAVITIES AND BRECCIA 



The spalling ofl of glass fragments, which may be expected to occur 

 in most cases — perhaps most actively in the water — partially fllls the 

 interspheroidal spaces with breccia, where such openings persist, owing 

 to the failure of the pillows to fit together perfectly. These spaces may 

 also contain fine sediment where the lava has flowed into soft mud or 

 ooze under water, or sediment of any kind may be subsequently washed 

 into the interstices from above, whether the flow is subaqueous or sub- 

 aerial. Occasionally a growing pillow may crack during its expansion 

 in such a manner as to spill a portion of its liquid contents into the 

 spaces between underlying or adjacent pillows. Thus, for example, in 

 some of the Carboniferous pillow basalts of Fife and Kinross, Scotland, 

 lava similar to that of the pillows has filled a part of the openings. 



