The last of the Harvard experiments that I took part in concerned melting up powders of basaltic minerals and rocks, letting them cool down gradually, and then sectioning them for the polarizing microscope to see how they resembled lavas. V. F. Marsters of the University of Indiana helped me. Based on the European work of Doelter, Fouqué, Michel-Lévy, and others, we used a French furnace with gas flame blast and small crucibles of diatomaceous earth mixed with clay. The specimen powders of crushed natural basalts, or mixtures of pyroxene, feldspar and olivine, were kept glowing for forty to 150 hours, and cooled either rapidly or slowly. The belief in those days was that slow cooling was the main control of coarse crystallization. Quick or slow cooling certainly does produce these effects in lava flows. From quick cooling, we generally got radial bunches of crystals or spherulites, in a glassy groundmass. From slow cooling, we got diabase structure or coarser crystallization, with some openwork hollow crystals. And there were little grains of magnetite and spinel. Much time was wasted on furnace safety and methods, and on fire-punctured crucibles of platinum, carbon, and graphite. Nothing had been learned in 1900 about stirring, nor about gas as an ingredient in basalt. It was not until years later, at the Hawaiian Volcano Observatory, that Emerson proved that aa lava was made by stirring a crucible. Aa is crystalline. Emerson got glassy lava by quiet melting. No one has yet subjected lava to hydrogen blasts like those of a Bessemer furnace, nor to other gases. There is a big field here for imitating Mauna Loa and Etna fountains, and for critical petrography of artificial basalts. Modern work has been concerned with physical chemistry of limited mineral systems. So far as I know, no one has mathematically synthesized natural rocks as an object in natural history since the work of Carl Barus for the U. S. Geological Survey in the nineties. CHAPTER III Expedition Decade “_The voice of thy thunder was in the whirlwind._” Whereas small scale experiments in the laboratory helped me to think about the details of nature’s experiments, there remained the need to measure nature itself. The deep lavas of South Dakota, squeezing among shale beds, posed many questions. What penetrating of strata goes on under Vesuvius? Does lava inrush tilt or lift the ground? Does this measure up to eruptions in or from craters? Cannot experiments with craters themselves be made by dwelling there? Certainly the progress of lavas can be measured as they flow forth.