An aeromagnetic map across the eastern and central United States between lats 37°N and 38°N reflects the regional structure and lithology of the magnetic crystalline rocks. The major crustal units that are delineated are the Appalachian Mountain system, the buried southwesterly extension of the Grenville province, the prominent fault zones across Kentucky, southern Illinois, and Missouri, the igneous rocks of the St. Francois Mountains and vicinity, and the buried belt of low-grade metamorphic rocks in southeastern Kansas. The map also reveals a series of conspicuous, essentially east-trending magnetic lineaments, anomaly trends, and breaks in anomaly pattern along the entire survey...