About a decade ago, Johns Hopkins University geologist Bruce Marsh challenged the century-old concept that the Earth’s outer layer formed when crystal-free molten rock called magma oozed to the surface from giant subterranean chambers hidden beneath volcanoes. Marsh’s theory ? that the deep-seated plumbing underneath volcanoes is actually made up of an extensive system of smaller sheet-like chambers vertically interconnected with each other and transporting a crystal-laden “magmatic mush” to the surface ? has become far more widely accepted. Now he proposes that Earth’s magma delivery system fractured the planet’s crust to provide a sort of “template,” guiding the sculpting of valleys and mountain ranges.