Figure F16. Close-up photograph of interval 183-1141A-21R-1, 20-34 cm, showing the transition between the vesicular upper crust and the massive interior of basement Unit 5. At this transition, note the horizontal vesicular sheet (arrows) with an undulating upper surface and flat bottom. The undulations contain large vesicles pushing up into the base of the upper crust and demonstrate that these megavesicles are derived from volatiles released during crystallization and segregation of late-stage melts.