The uppermost of the globule ignimbrite sheets of Mount Suswa in Kenya covers an area of about 300 km 2 and ranges in thickness from 25 cm to 2.5 m. It is welded and devitrified and exhibits gas-phase crystallization to an extent that is unusual for a sheet as thin as this. Most of the ignimbrite is composed of rounded ash particles, and the fine-ash fraction consists largely of ovoid and spherical globules. In the basal vitrophyric zone the globules are mostly nonvesicular and 20 to 75 μm in diameter, but in the devitrified part of the sheet they are inflated to form bubbles. Lapilli in the vitrophyric zone are chiefly of obsidian, which is inflated to form pumice in the devitrified zone. Most of the obsidian is characterized by a wavy banding, some of which is a relict welded tuff texture. We have no satisfactory explanation for the banded globules, which originated neither from melting of cuspate shards, nor condensation from vaporized magma, nor in a spray or fountaining of magma. Many of the globules exhibit undeformed banding similar to that in the obsidian, indicating that they originated in essentially their present shape either from larger particles such as lapilli or from a partially remelted welded tuff that yielded both lapilli and ash. Welded-tuff textures in the obsidian lapilli are also difficult to explain and seem to indicate a complex eruptive or emplacement process, which could possibly involve discharge of molten agglutinate from an earlier eruption.