Note 9 — Chapter V · GALAPAGOS ARCHIPELAGO.

The irregular and angular form of the vesicles is probably caused by the unequal yielding of a mass composed, in almost equal proportion, of solid crystals and of a viscid base. It certainly seems a general circumstance, as might have been expected, that in lava, which has possessed a high degree of fluidity, as well as an even-sized grain, the vesicles are internally smooth and spherical.