The recent notion that radioactivity heat is in the outer shell denies contraction of the inner earth. Furthermore, I do not believe in a shallow underlayer of lava fifty or less miles down and capable of flowing horizontally under shifting weight. I do believe in a deep underlayer of fluid 1,800 miles down, under a block-faulted crust. This fluid core adjusted itself to the ocean-bottom blocks originally, making the upright slices moving-down controllers of the Appalachian basin. There is no proof that sediment weight did it. It is more likely that igneous, or fire-made, lava, as the thick outer armor plate of the globe erupted in acts of intrusion, lubricated the vertical slices. Intrusions are under every sedimentary mountain range on earth. It is more likely that an agelong up of ridge fault blocks and a down of the basin fault blocks decided where the central continental basin should be, all of it well within the permanent side ridges of North America. For this was a continental mediterranean sea, and the warping of its highland of Philadelphia and its basin of Cincinnati was a mere episode in the 2,000 million year history of Atlantic and Pacific borders of the continent. The sinking of the intracontinental sea, relative to the staying up of the highlands, was a wave in the history of globe and core. Erosion and deposition were results, not causes. They were results of the volcanic history of the ever moving active mosaic of the globe. The permanent North America remained high, relative to Atlantic and Pacific deeps.
The folding of the sediments merges into intrusions of magma in the southern Appalachians. Here arose the granite problem on a tremendous scale, which is repeated in our Ascutney Mountain in Vermont. What it was doing under the bottom of those vast fields of limestone from Ohio to Illinois we have no idea. No more do we know what is doing under the vast fields of lime and red ooze at the present bottoms of the deep oceans. But we do know that fire-made rock squirts up under all sea-laid sediments which anyone has ever studied on islands or continents. This fire-made rock, solidified, has thickness and a bottom. We do not know its thickness nor its bottom. We do know that under it are big cracks 2,000 miles long rupturing it into volcano systems. The conclusion is that the globe is mantled by a layer of igneous matter which has spouted up cracks since more than 3,000 million years ago. How did this matter migrate by new intrusions, to pull, push, heat, and wrinkle through 500 million years the dirt accumulated in shallow Appalachian trenches from Alabama to Indiana? We do not know.
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.
The decade following my mud-pie experiments saw me assistant professor at Harvard and head professor of the geological department at Massachusetts Institute of Technology. These appointments were under Presidents Eliot, Pritchett, and Maclaurin. From 1901 to 1910 I continued to serve the Geological Survey, writing up back reports. Then nature took a hand. Along came earthquakes and eruptions in Guatemala, a terrific disaster in the West Indies, expeditions to the Caribbees, Italy, the Aleutian Islands, Japan, Hawaii, and Central America, another in north Japan, and disastrous earthquakes at San Francisco, Valparaiso, Messina, and Costa Rica. The destruction of St. Pierre in Martinique set the stage for field work on volcanoes and earthquakes, work which I was to continue for a half century.