Verlag: United States Government Printing Office, Washington, 1975
Zustand: very good. from the abstract, "The Shallow parts of geothermal systems are important for the understanding of total systems, but commercial geothermal drilling has focused almost entirely on target depths of 2,000 ft. and more." dx4. softcover, 11.5" x 9", 70 pages, indexed, illustrated, creased rear top cover2.25 penciled on front cover.